here, i couldn't get the A,B,C values while using if, elseif conditions. how to get values while using conditional statement?

dx=0.05; dy=0.25; dt=0.2;
for j=1:n
    if i==2:m
        C(i)=V(i,j)*dt/4*dy-dt/2*(dy)^2;
    elseif i==1:m-1
        A(i)=-V(i,j)*dt/4*dy-dt/2*(dy)^2;
    elseif i==1:m
        B(i)=1+U(i,j)*dt/2*dx+dt/(dy)^2;
    end
end

[Dyuman Joshi]

Are the variables i and m been defined? What are their values?

Additionally, if you want to compare arrays, use isequal or use tolerance based comparison with all.

[Arif Hoq]

what is the value of n and i ?

[Yanni]

i, j are the x and y directions respectively.,and m and n are the no.grids so m =20 and n =80

[Dyuman Joshi]

You still haven't answered - What is the value of i? Is there a value to i?

What exactly are you trying to achieve from this code?

[Torsten]

@Gayathri comment moved here:

yes, m = 20; but im not comparing values i want find temperature profile like tridaigonal system

Answer 1

[Jan]

This cannot work:

if i==2:m    

2:m is a vector. You can compare i with the vector, but the == operator works elementwise. The if command requires a scalar condition, such that Matlab inserts an all() implicitly here. But all(i == 2:m) is only true, if i is set to 2:m.

The same concerns the elseif conditions.

The values of A(i), B(i) and C(i) are overwritten in each iteration of the outer loop.

The explanation "i want find temperature profile like tridaigonal system" is not enough to explain clearly, what your code should do. Seeing a failing code does not allow to guess its intention also.

What is the desired output for A, B, C? Vectors or matrices? Maybe you want:

C(2:m, 1:n) = V(2:m, 1:n)*dt/4*dy-dt/2*(dy)^2;

without a loop and if command.