daviddoria's profile - activity

Say I have something like this:

var('a','b','c')
test=b*a + c*a + 3*a + b + c

I can find that the coefficient of 'a' is (b+c+3) using:

test.coefficient(a,1)

However, I am interested in find the coefficient of $ab$ (which in this case would just be $1$). I tried

test.coefficient(a*b,1)

but it just returns zero. Is something like this possible?

I also have a system that Sage cranks and cranks on but never returns an answer: var('r,s,m,n,l,A,B,C,D,E,F') solve([2*m - 2*r==2*A*m*l + B*n*l + D*l, 2*n-2*s==B*m*l + 2*C*l*n + E*l, A*m + B*m*n + C*n^2 + D*m + E*n + F == 0], m, n, l) Any thoughts as to why this happens?