Based on the equation that you have provided, the code for the equation goes like :
syms g x y w k i c chi
diff(g,z) = (i*c/(2*w))*(diff(g,x,2) + diff(g,y,2)) + 2*i*pi*k*chi*g;
Note: In this code, the syms function is used to define symbolic variables, the diff function is used to compute partial derivatives.
