Error: File: square_matrix.m Line: 12 Column: 16

Hello I am trying to apply the rule:(S(i,j))^t = (S(i,j-1))^t+ (S(i-1,j))^t+ (S(i,j))^t + (S(i+1,j))^t + (S(i,j+1))^t

I am getting an error for entering the matrix incorrectly. Below is my full code. clear; clc; clf; disp('Starting...');

    S=zeros(50);

    newS=zeros(50);
    %i=0:5;
    %j=0:5;
    for t=1:200
        for i= 1:5
            j= 1:5
        (S(i,j))^t = (S(i,j-1))^t+ (S(i-1,j))^t+ (S(i,j))^t + (S(i+1,j))^t + (S(i,j+1))^t;
        if  0<=S(i,j)< 3
        then S(i,j)=0
        elseif 3<= S(i,j)<= 5
        then S(i,j)=1
        end
        end
        newS=S(i,j)
    end
    spy(newS)

actual error when run: ??? Error: File: square_matrix.m Line: 12 Column: 16 The expression to the left of the equals sign is not a valid target for an assignment.

Please advise.

Answer 1

[Jan]

What do you expect "^t" to do? It means "power to t". If you want to transpose a matrix, swap the indices instead.

The error message means, that you cannot apply a function on the left hand side of an assignment.

After you have fixed this, the next problems will appear:

if  0<=S(i,j)< 3

In Matlab this calculates:

S(i,j) < 3 ==> TRUE or FALSE
0 <= TRUE or FALSE

which is TRUE always, because TRUE is evaluated as 1 and FALSE as 0. You want:

if  0 <= S(i,j) && S(i,j) < 3

In addtion there is no then keyword in Matlab.

What are you expecting as result of these lines:

        for i= 1:5
            j= 1:5

?

The line:

newS=S(i,j)

overwrites the matrix newS in the first iteration and replaces the scalar value in all subsequent iterations. Therefore newS is a scalar at the end. Do you want newS(i, j)?

Finally I think the shown code is far away from a valid Matlab syntax. I suggest to read the Getting Started chapters of the documentation to learn the basics of this powerful programming language.