Why does my code not work?

Question

Why does the following code not work?

t=1;h=0.1;n=t/h+1;m=3;
W=Table[0,{n},{m+1}];
for[k=2,k<m+1,k++,
  f=Table[0,{n-2},{n-2}];
  f[[1,1]]=2-1/(1+10*h)+10*h*h*W[[2,k]];f[[1,2]]=-1+5*h;
  for[i=2,i<n-2,i++,
    f[[i,i]]=2+10*h*h*W[[i+1,k]];
    f[[i,i-1]]=-1-5*h;
    f[[i,i+1]]=-1+5*h;];
    f[[n-2,n-2]]=5*h+1+10*h*h*W[[n-1,k]];
  f[[n-2,n-3]]=-1-5*h;
  F=Table[0,{n-2}];
  for[i=1,i<n-1,i++,
    F[[i]]=
      -W[[i+2,k]]+2*W[[i+1,k]]-W[[i,k]]+
      5*h*(W[[i+2,k]-W[[i,k]])+
      5*h*h*W[[i+1,k]]*W[[i+1,k]];];

A=Linear Solve[f,-F];
for[i=2,i<n,i++,
   W[[i,k+1]]=W[[i,k+1]]+A[[i]]];
   W[[1,k+1]]=(W[[2,k+1]]+50*h)/(10*h+1);
   W[[n,k+1]]=W[[n-1,k+1]]];

There are syntax errors in your code. Use For not for; LinearSolve not Linear Solve; and there is a extra ] in last For-loop. — m_goldberg, Dec 10 '19 at 05:03
F comes out as {0, 0, 0, 0, 0, 0, 0, 0, 0} because there is no code to populate W, — m_goldberg, Dec 10 '19 at 05:20
In the last inner For-loop, (W[[i + 2, k] - W[[i, k]]) should be (W[[i + 2, k]] - W[[i, k]]) — m_goldberg, Dec 10 '19 at 05:25

m_goldberg · Answer 1 · 2019-12-10T06:17:03.813

1

This may be a partial answer. As I understand it your elaborate calculation of f can be replaced with:

t = 1;
h = 1/10;
n = t/h + 1;
f = 
  SparseArray[{Band[{1, 2}] -> -1/2, Band[{1, 1}] -> 2, Band[{2, 1}] -> -3/2}, n - 2]
f[[1, 1]] = f[[-1, -1]] = 3/2;
f // MatrixForm

edited Dec 10 '19 at 06:17

answered Dec 10 '19 at 05:58

m_goldberg

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Why does my code not work?

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