Matrix dimensions must agree

Hi! Mi program show me a mistake with my matrix but both have nine values in x and y.

Answer 1

[Tommy]

A is a 4x9 array, so A' is a 9x4 array.

A.*A'

This tries to use element-wise multiplication on A and A', but they aren't the same size (or compatible), so you get an error.

Maybe you mean this?

a=A*A'\A*y';

This performs matrix multiplicaton on A and A', resulting in a 4x4 array which you can then pass to mldivide along with A*y' (a 4x1 array).