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350 lines
9.1 KiB
R
350 lines
9.1 KiB
R
## Time-stamp: "Last modified 2022-12-21 13:47:00 delucia"
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## Brutal implementation of 2D ADI scheme
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## Square NxN grid with dx=dy=1
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ADI <- function(n, dt, iter, alpha) {
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nx <- ny <- n
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dx <- dy <- 1
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field <- matrix(0, nx, ny)
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## find out the center of the grid to apply conc=1
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cen <- ceiling(n/2)
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field[cen, cen] <- 1
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## prepare containers for computations and outputs
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tmpX <- tmpY <- res <- field
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out <- vector(mode="list", length=iter)
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for (it in seq(1, iter)) {
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for (i in seq(1, ny))
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tmpX[i,] <- SweepByRow(i, res, dt=dt, alpha=alpha)
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resY <- t(tmpX)
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for (i in seq(1, nx))
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tmpY[i,] <- SweepByRow(i, resY, dt=dt, alpha=alpha)
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res <- t(tmpY)
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out[[it]] <- res
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}
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return(out)
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}
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## Workhorse function to fill A, B and solve for a given *row* of the
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## grid matrix
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SweepByRow <- function(i, field, dt, alpha) {
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dx <- 1 ## fixed in our test
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A <- matrix(0, nrow(field), ncol(field))
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Sx <- Sy <- alpha*dt/2/dx/dx
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## diagonal of A at once
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diag(A) <- -1-2*Sx
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## adjacent diagonals "Sx"
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for (ii in seq(1, nrow(field)-1)){
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A[ii+1, ii] <- Sx
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A[ii, ii+1] <- Sx
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}
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B <- numeric(ncol(field))
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## We now distinguish the top and bottom rows
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if (i == 1) {
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## top boundary, "i-1" doesn't exist or is at a ghost
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## node/cell boundary (TODO)
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for (ii in seq_along(B))
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B[ii] <- (-1 +2*Sy)*field[i,ii] - Sy*field[i+1,ii]
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} else if (i == nrow(field)) {
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## bottom boundary, "i+1" doesn't exist or is at a ghost
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## node/cell boundary (TODO)
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for (ii in seq_along(B))
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B[ii] <- -Sy*field[i-1, ii] + (-1 +2*Sy)*field[i,ii]
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} else {
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## inner grid row, full expression
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for (ii in seq_along(B))
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B[ii] <- -Sy*field[i-1, ii] + (-1 +2*Sy)*field[i,ii] - Sy*field[i+1,ii]
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}
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x <- solve(A, B)
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x
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}
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DoRef <- function(n, alpha, dt, iter) {
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require(ReacTran)
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require(deSolve)
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N <- n # number of grid cells
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XX <- n # total size
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dy <- dx <- XX/N # grid size
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Dy <- Dx <- alpha # diffusion coeff, X- and Y-direction
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## The model equations
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Diff2D <- function (t, y, parms) {
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CONC <- matrix(nrow = N, ncol = N, y)
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dCONC <- tran.2D(CONC, D.x = Dx, D.y = Dy, dx = dx, dy = dy)$dC
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return (list(dCONC))
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}
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## initial condition: 0 everywhere, except in central point
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y <- matrix(nrow = N, ncol = N, data = 0)
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cen <- ceiling(N/2)
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y[cen, cen] <- 1 ## initial concentration in the central point...
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## solve for time units
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times <- seq(0,iter)*dt
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out <- ode.2D (y = y, func = Diff2D, t = times, parms = NULL,
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dim = c(N,N), lrw=155412)
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ref <- matrix(out[length(times),-1], N, N)
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return(ref)
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}
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## test number 1
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adi1 <- ADI(n=25, dt=100, iter=50, alpha=1E-3)
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ref1 <- DoRef(n=25, alpha=1E-3, dt=100, iter=50)
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plot(adi1[[length(adi1)]], ref1, log="xy", xlab="ADI", ylab="ode.2D (reference)",
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las=1, xlim=c(1E-15, 1), ylim=c(1E-15, 1))
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abline(0,1)
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sapply(adi1, sum)
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## test number 2
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adi2 <- ADI(n=51, dt=10, iter=200, alpha=1E-3)
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ref2 <- DoRef(n=51, alpha=1E-3, dt=10, iter=200)
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plot(adi2[[length(adi2)]], ref2, log="xy", xlab="ADI", ylab="ode.2D (reference)",
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las=1, xlim=c(1E-15, 1), ylim=c(1E-15, 1))
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abline(0,1)
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## Test heterogeneous scheme, chain rule
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ADIHet <- function(field, dt, iter, alpha) {
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if (!all.equal(dim(field), dim(alpha)))
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stop("field and alpha are not matrix")
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## now both field and alpha must be nx*ny matrices
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nx <- ncol(field)
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ny <- nrow(field)
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dx <- dy <- 1
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## find out the center of the grid to apply conc=1
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cenx <- ceiling(nx/2)
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ceny <- ceiling(ny/2)
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field[cenx, ceny] <- 1
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Aij <- Bij <- alpha
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for (i in seq(2,ncol(field)-1)) {
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for (j in seq(2,nrow(field)-1)) {
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Aij[i,j] <- (alpha[i+1,j]-alpha[i-1,j])/4 + alpha[i,j]
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Bij[i,j] <- (alpha[i,j+1]-alpha[i,j-1])/4 + alpha[i,j]
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}
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}
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if (any(Aij<0) || any(Bij<0))
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stop("Aij or Bij are negative!")
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## prepare containers for computations and outputs
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tmpX <- tmpY <- res <- field
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out <- vector(mode="list", length=iter)
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for (it in seq(1, iter)) {
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for (i in seq(1, ny))
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tmpX[i,] <- SweepByRowHet(i, res, dt=dt, alpha=alpha, Aij, Bij)
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resY <- t(tmpX)
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for (i in seq(1, nx))
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tmpY[i,] <- SweepByRowHet(i, resY, dt=dt, alpha=alpha, Bij, Aij)
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res <- t(tmpY)
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out[[it]] <- res
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}
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return(out)
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}
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## Workhorse function to fill A, B and solve for a given *row* of the
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## grid matrix
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SweepByRowHet <- function(i, field, dt, alpha, Aij, Bij) {
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dx <- 1 ## fixed in our test
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Sx <- Sy <- dt/2/dx/dx
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## diagonal of A at once
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A <- matrix(0, nrow(field), ncol(field))
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diag(A) <- 1+2*Sx*diag(alpha)
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## adjacent diagonals "Sx"
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for (ii in seq(1, nrow(field)-1)) {
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A[ii+1, ii] <- -Sx*Aij[ii+1,ii]
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A[ii, ii+1] <- -Sx*Aij[ii,ii+1]
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}
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B <- numeric(ncol(field))
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## We now distinguish the top and bottom rows
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if (i == 1) {
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## top boundary, "i-1" doesn't exist or is at a ghost
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## node/cell boundary (TODO)
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for (ii in seq_along(B))
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B[ii] <- Sy*Bij[i+1,ii]*field[i+1,ii] + (1-2*Sy*Bij[i,ii])*field[i, ii]
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} else if (i == nrow(field)) {
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## bottom boundary, "i+1" doesn't exist or is at a ghost
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## node/cell boundary (TODO)
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for (ii in seq_along(B))
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B[ii] <- (1-2*Sy*Bij[i,ii])*field[i, ii] + Sy*Bij[i-1,ii]*field[i-1,ii]
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} else {
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## inner grid row, full expression
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for (ii in seq_along(B))
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B[ii] <- Sy*Bij[i+1,ii]*field[i+1,ii] + (1-2*Sy*Bij[i,ii])*field[i, ii] + Sy*Bij[i-1,ii]*field[i-1,ii]
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}
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x <- solve(A, B)
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x
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}
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## adi2 <- ADI(n=51, dt=10, iter=200, alpha=1E-3)
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## ref2 <- DoRef(n=51, alpha=1E-3, dt=10, iter=200)
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n <- 51
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field <- matrix(0, n, n)
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alphas <- matrix(1E-3*runif(n*n, 1,1.2), n, n)
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## for (i in seq(1,nrow(alphas)))
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## alphas[i,] <- seq(1E-7,1E-3, length=n)
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#diag(alphas) <- rep(1E-2, n)
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adih1 <- ADIHet(field=field, dt=10, iter=100, alpha=alphas)
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adi2 <- ADI(n=n, dt=10, iter=100, alpha=1E-3)
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par(mfrow=c(1,3))
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image(adi2[[length(adi2)]])
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image(adih1[[length(adih1)]])
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points(0.5,0.5, col="red",pch=4)
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plot(adih1[[length(adih1)]], adi2[[length(adi2)]], pch=4, log="xy")
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abline(0,1)
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sapply(adih1, sum)
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sapply(adi2, sum)
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adi2
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par(mfrow=c(1,2))
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image(alphas)
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image(adih1[[length(adih1)]])
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points(0.5,0.5, col="red",pch=4)
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## Test heterogeneous scheme, direct discretization
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ADIHetDir <- function(field, dt, iter, alpha) {
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if (!all.equal(dim(field), dim(alpha)))
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stop("field and alpha are not matrix")
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## now both field and alpha must be nx*ny matrices
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nx <- ncol(field)
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ny <- nrow(field)
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dx <- dy <- 1
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## find out the center of the grid to apply conc=1
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cenx <- ceiling(nx/2)
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ceny <- ceiling(ny/2)
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field[cenx, ceny] <- 1
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## prepare containers for computations and outputs
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tmpX <- tmpY <- res <- field
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out <- vector(mode="list", length=iter)
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for (it in seq(1, iter)) {
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for (i in seq(2, ny-1)) {
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Aij <- cbind((alpha[i,]+alpha[i-1,])/2, (alpha[i,]+alpha[i+1,])/2)
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Bij <- cbind((alpha[,i]+alpha[,i-1])/2, (alpha[,i]+alpha[,i+1])/2)
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tmpX[i,] <- SweepByRowHetDir(i, res, dt=dt, Aij, Bij)
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}
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resY <- t(tmpX)
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for (i in seq(2, nx-1))
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tmpY[i,] <- SweepByRowHetDir(i, resY, dt=dt, Bij, Aij)
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res <- t(tmpY)
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out[[it]] <- res
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}
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return(out)
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}
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## Direct discretization, Workhorse function to fill A, B and solve
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## for a given *row* of the grid matrix
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SweepByRowHetDir <- function(i, field, dt, Aij, Bij) {
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dx <- 1 ## fixed in our test
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Sx <- Sy <- dt/2/dx/dx
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## diagonal of A at once
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A <- matrix(0, nrow(field), ncol(field))
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diag(A) <- 1 + Sx*(Aij[,1]+Aij[,2])
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## adjacent diagonals "Sx"
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for (ii in seq(1, nrow(field)-1)) {
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A[ii+1, ii] <- -Sx*Aij[ii,1]
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A[ii, ii+1] <- -Sx*Aij[ii,2]
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}
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B <- numeric(ncol(field))
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for (ii in seq_along(B))
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B[ii] <- Sy*Bij[ii,2]*field[i+1,ii] + (1 - Sy*(Bij[ii,1]+Bij[ii,2]))*field[i, ii] + Sy*Bij[ii,1]*field[i-1,ii]
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x <- solve(A, B)
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x
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}
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## adi2 <- ADI(n=51, dt=10, iter=200, alpha=1E-3)
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## ref2 <- DoRef(n=51, alpha=1E-3, dt=10, iter=200)
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n <- 51
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field <- matrix(0, n, n)
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alphas <- matrix(1E-3*runif(n*n, 1,1.2), n, n)
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## for (i in seq(1,nrow(alphas)))
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## alphas[i,] <- seq(1E-7,1E-3, length=n)
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#diag(alphas) <- rep(1E-2, n)
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adih <- ADIHetDir(field=field, dt=10, iter=100, alpha=alphas)
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adi2 <- ADI(n=n, dt=10, iter=100, alpha=1E-3)
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par(mfrow=c(1,3))
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image(adi2[[length(adi2)]])
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image(adih[[length(adih)]])
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points(0.5,0.5, col="red",pch=4)
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plot(adih1[[length(adih1)]], adi2[[length(adi2)]], pch=4, log="xy")
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abline(0,1)
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sapply(adih, sum)
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sapply(adi2, sum)
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adi2
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par(mfrow=c(1,2))
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image(alphas)
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image(adih1[[length(adih1)]])
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points(0.5,0.5, col="red",pch=4)
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