Matrix Help

I have a matrix similar to the following

C = 1 2 4 5
    3 4 5 6
    6 4 2 1

each of these values have been calculated as a function of x and y. Say

        x = a b c d
        y = f g h

This corresponds to x as so

C = 1(f, a) 2(f, b) 4(f, c) 5(f, d)
    3(g, a) 4(g, b) 5(g, c) 6(g, d)
    6(h, a) 4(h, b) 2(h, c) 1(h, d)

Say I want to get the corresponding x and y values for a value in C, how would I do this?

[Jan]

The question is not getting clear to me.

E.g. if you have 6 as input, what is the expected output? What do the symbols "a", "b", "c" etc mean? Are they numbers, indices, symbolic expressions, functions?

Answer 1

[David Young]

As Jan comments, your question is not clear. Like him, I can't understand the role of the symbols a, b etc. which just seem to correspond to the subscripts for the matrix, with a=1, b=2, c=3, d=4, f=1, g=2, h=3. If so, they are redundant, and it's simpler to use numerical subscripts.

Guessing a bit, perhaps your question is simply asking what the subscripts are for a particular value in C. So C(3) is at x=1, y=2. If that's right, the answer is this:

[y, x] = find(C == 3)

which returns the x and y coordinates for the value 3. Note the reversal in order of y and x in the results list. If you use 6 rather than 3 you will get vectors for x and y each with 2 subscripts, because 6 is found at x=4,y=2 and also at x=1,y=3.

If you were asking something more complex, please clarify.

Answer 2

[Andrei Bobrov]

e.g.

i1 =[4    16    14    11]

j1 =[8     1     4]

x =[5    -6    -2     2
    0   -11    -8    -4
    6    -8    -8    -6]

f1 = @(i1,j1)bsxfun(@minus,bsxfun(@plus,x,i1),j1')

C = f1(i1,j1)