# Momentum sources¶

You can add additional momentum sources to the simulations which can be useful for MMS testing (Method of Manufactured Solutions). An example from the variable density disk test case included in the Ocellaris source code repository can be seen below (this MMS test was taken from [GS11]).

momentum_sources:
-   name: MMS
degree: 2
cpp_code:
-   Q*nu*sin(sin(t))*cos(t) - (x[0]*cos(t)*cos(t) - x[1]*sin(t))*(Q*sqrt(x[0]*x[0] + x[1]*x[1])*cos(sin(t) - atan2(x[1], x[0])) + 1 + Q) + sin(t)*sin(x[1])*cos(x[0])
-   -Q*nu*cos(t)*cos(sin(t)) - (x[0]*sin(t) + x[1]*cos(t)*cos(t))*(Q*sqrt(x[0]*x[0] + x[1]*x[1])*cos(sin(t) - atan2(x[1], x[0])) + 1 + Q) + sin(t)*sin(x[0])*cos(x[1])

degree

The polynomial degree of the function used to represent the momentum source C++ expression