Excel - help with eulers method on coupled equations

[ragga puffin]

im doing a simulation on a magnetic moment in a magnetic field B and I am quite stuck.

its a set of coupled equations: m'-x=B*m-y & m'-y= - B*m-x
where m-x is the x component, ' is rate of with respect to time etc.
the vector should be precessing in a circle with frequency w= - B, B is set to one so it should make one rotation in one second -> full cycle -> full sine wave, but i seem to only be getting about half a sine wave

the cosine term in the m'-y formula can be neglected, as can the m'-z and m-z columns because the starting point is M'= M X B (the cross product of the moment and the magnetic field) and B is defined as being in the z direction.

im pretty sure the equations are right and the problem lies in my formulae in excel, any help will be greatly appreciated:!)

 

[berkeman]

I filled the data for mx down past 1.5 seconds and plotted it, and it looks reasonable except for the expected period that you mention. How did you derive that the period should be 1? Is there maybe a factor of PI missing? It looks like the period is actually closer to PI...