Defining matrix variable to get numerical solution to the Winkler foundation differential equation

Following the solution to the differential equation for the deflection curve of a beam on an elastic foundation, am trying to get the bending moment M and shearing force V based on the 2nd- and 3rd-order derivatives (using MathCad prime 9).

I can come up with values based on the derivative expression BUT am unable to assign the results to matrix variables M and V for plotting the results to show variation along the length of the beam.

I tried to define matrices with matching size, BUT it won't evaluate the differential equation.

I alternatively tried for loop, BUT the same issue persists. The v counter does not increment to allow calculation of the M variable.

Should I be using the ODE solvers for this? Am I missing something? Can't seem to figure it out.

Thank you for the help.