2017-08-03 19:21:25 +0100 commented answer how can i define a matrix product like a summation Thank you so much this is exactly i want 2017-08-03 09:01:55 +0100 asked a question how can i define a matrix product like a summation first, my mother tongue is not English but I try it, my problem is that if I define a symbolic matrix V such that, var('V_11,V_12,V_13,V_21,V_22,V_23,V_31,V_32,V_33') V = matrix(SR,3,3,[V_11,V_12,V_13,V_21,V_22,V_23,V_31,V_32,V_33])  and then I define P = [V[a,k]*V[b,k]*V[a,j]*V[b,j] for k in [0,1,2] for j in [0,1,2]]  But if I evaluate, for example P(a=0,b=1)  but the code is not work can someone help me?