How in Matlab?

How to set up a program that introduces a square matrix of numbers from the fourth line? The program should be replaced first positive element in each row 1 and outputting the resulting matrix. Go somewhere and ... Please help!

[James Tursa]

Please provide a short example of inputs and desired outputs.

[Mario Marinov]

Let matrix is >> A=[1 2 3;4 5 6;7 8 9]

A =

     1     2     3
     4     5     6
     7     8     9
The program to replace the first numbers in each row, if they are positive, with the number 1. Then put the newly matrix :)

Answer 1

[Star Strider]

I’m not certain what you want. See if this works:

A=[1 2 3;4 5 6;7 8 9];
A(A(1,:)>0) = 1;

It tests the first column in every row, and if it is positive, replaces it with 1.

[Mario Marinov]

This works! Thanks! My record is wrong:

>> A(1,:)>0=1
 A(1,:)>0=1
         |
Error: The expression to the left of the equals sign is not a valid target for an assignment.

[Star Strider]

You have to put parentheses in the subscript references:

A(A(1,:)>0) = 1;

Answer 2

[Mario Marinov]

Excuse me, but if the matrix is this: >> A = [-1 2 3;4 -5 6;7 8 -9]

A =

    -1     2     3
     4    -5     6
     7     8    -9
How to replace the first positive number in each row, and not in the first column with 1?

[Star Strider]

With those conditions, the code requires a loop and the find function:

A = [-1 2 3;4 -5 6;7 8 -9];
for k1 = 1:size(A,1)
    A(k1,find(A(k1,:)>0, 1, 'first')) = 1;
end

[Mario Marinov]

Working again! Thanks!

[Star Strider]

My pleasure!