## 45 Reputation

11 years, 251 days

## code for tri diagonal matrix...

I want to make tridaigonal matrix like this for n x m order

[3  2  0  0  0  0]

[1  3  1  0  0  0]

[0  1  3  1  0  0]

[0  0  1  3  1  0]

[0  0  0  1  3  1]

[0  0  0  0  2  3]

## how to write system of linear equations ...

hi friends i have already asked help related to this code which am gona post but this time I am facing some different problem. In the worksheet which i attached below is having algorthim for cubic spline on heat equation. IN this sheet FD equation is my main equation and i want this equation to use boundary conditions mention in code. After using that i want this equation to generate system of linear equations when i=0..M, j=1..N. But i dont want to solve it completely. After...

## how to find values on internal nodes of ...

hi friends..!!
I am working on 1d heat equation with finite difference method and i have made rough code for it in which i considered mesh size of 4 in x direction as wel as in time space. By initial condition am known with points (0,0) (1,0) (2,0) (3,0) and (4,0). AS boundary conditions are neumman as u can see in code below i have attached. Now my problem is loops in end of program is not picking internal nodes like (1,1), (1,2), (1,3),(1,4), (2,1),...,(4,4). So please...

## problem in loops......

hi friends am trying code for 1d heat equation but my code is not giving me result which i needed...although its running but still am in doubt its not picking boundary conditions and initial condition in last loop of discritzed equation due to which my result are totally wrong.. am attaching worksheet please let me know where am wrong...will_see.mw

## error in graph ploting...

am using this command in end of my code

`> Points := [seq(seq([x[i], y[j], U[i, j]], i = 0 .. M-1), j = 0 .. N)];> Points1 := subs({BC, XY, op(SOL)}, Points);> pointplot3d(Points1, symbol = solidsphere, labels = [x, y, U], shading = zhue, orientation = [50, 70], axes = boxed);`
`but at last line am getting error`
`Error, (in plots/pointplot) incorrect first argument `
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