variable needs to be array but only returning 1 value

I have a code that I am trying to vectorize but I must be missing something:

This code below is part of a bigger loop, but I think that is irrelevant for this:

    r = 1:0.01:2;
    g_fit = g(r,mat(bnd(k),3));
    plot(r,g_fit,'k');
    xlabel('r');
    ylabel('g(r,\eta)');
    hold on;

For some reason, g_fit only contains a single value. I tried putting parenthesis around the r in the call the function g, but that didn't help either. How can I get g to be a matrix that stores the result as r goes from 1 to 2 in increments of 0.01?

Here are the two functions:

function rdf = g(x,rpf)
    rdf = x/((1+C(rpf)*(x-1)).^3);
end

function C_function = C(rpf)
    B1 = 1.90322581;
    B2 = 2.13209879;
    B3 = -2.45289889;
    C_function = (1.0+rpf*(B1+rpf*(B2+rpf*B3)))/(3.0*(1-rpf));
end

Answer 1

[Walter Roberson]

Your r is a vector. You are passing that in as the first parameter of g, where it is known as x.

In g you have x/(an expression in x) . That is a matrix-right-divide request of a 1 x 101 by a 1 x 101 . Matrix right divide produces a result with a number of rows equal to the number of rows in the numerator (1 in this case) and number of columns equal to the number of rows in the denominator (1 in this case), so you get a 1 x 1 result.

Are you sure you want to do a fitting process? Would it perhaps make more sense to use element-by-element division, ./ instead of / ?

[Stephen23]

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html