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I am guessing that you want to multiply B (that seems to be a [10 x 2] matrix) and X (that seems to be a [10 x 1] vector). That will not work because the number of columns of B has to equal the number of rows in X.
If you define B as [2 x 10], then the [2 x 1] vector Y will be:
Y = B*X
Also, please do not use ‘i’ and ‘j’ for array indexing. MATLAB uses those for its imaginary operators. They will work as array indexes but will cause confusion if you also use complex numbers.