How can I set a matrix value to equal a non-numeric coordinate?

For example, if part of a matrix equals 3, I want that coordinate to be (a,b). Then I want to be able to use that coordinate to change other values, such as writing (a,b+1)=4, to change the value in the next column to 4, or (a-1,b)=7 to change the value in the row above to 7.

Thanks.

This is what I've attempted and doesn't work:

clear, clc

x = randi(10,10);
x(x==3) = x(a,b);

Undefined function or variable 'a'.

Error in Lab4 (line 4)

x(x==3)=x(a,b);

[madhan ravi]

Example with an illustration.

Answer 1

[madhan ravi]

[a,b]=find(x==3)% I don't see the point of this if your assigning the same value
x==3 % is already sufficient and efficient for indexing

[Liam Vella]

When I write

clear, clc
x = randi(10,10);
[a,b] = find(x==3)
[a-1,b] = 7;

It doesn't work and the coordinate is not set to equal 7,

Why?

[madhan ravi]

What is that your trying to do ? Write your expected result explicitly with a 3 by 3 matrix. the expression a-1 will error out if a is one.