On Thu, Feb 21, 2013 at 8:11 PM, Aaron Meurer <[email protected]> wrote: > This is a bug. See > https://code.google.com/p/sympy/issues/detail?id=2616. We need to > modify Expr.__pow__ to accept the ternary pow. It should be > relatively easy. In the general case, it should return Mod(a**b, n), > but it should be special cased for Integer (and maybe Rational)? so > that it can be calculated efficiently, using the builtin pow on > builtin ints. > > The workaround is to convert everything to int before passing it to pow.
Thanks Aaron! I'm testing the module now... > > Aaron Meurer > > On Wed, Feb 20, 2013 at 7:43 PM, David Joyner <[email protected]> wrote: >> Hi: >> >> The program below works fine: >> >> def matrix_inverse_mod(K, m): >> """ >> Returns the inverse of the matrix K mod m, if it exists. >> >> Matrix inverse of K mod m: >> - Compute `adj(K) = cof(K)^t`, the adjoint matrix of K. >> - Compute `r = 1/det(K) mod m`. >> - `K^(-1) = r*adj(K) mod m`. >> >> Examples >> ======== >> >> >>> A = Matrix(2, 2, [1, 2, 3, 4]) >> >>> print matrix_inverse_mod(A, 3) >> [ 8, -4] >> [-6, 2] >> >> """ >> from sympy import Matrix, gcd >> from sympy.ntheory import totient >> phi = totient(m) >> det_K = K.det() >> if gcd(det_K, m) != 1: >> raise ValueError('Matrix is not invertible (mod %d)'%m) >> # pow(det_K, phi-1, m) raises a __sympifyit_wrapper() error, so ... >> det_inv = pow(det_K, phi-1)%m >> K_adj = K.cofactorMatrix().transpose() >> K_inv = det_inv*K_adj >> return K_inv >> >> >> However, if you do the intelligent thing and use >> >> def matrix_inverse_mod(K, m): >> """ >> Returns the inverse of the matrix K mod m, if it exists. >> >> Matrix inverse of K mod m: >> - Compute `adj(K) = cof(K)^t`, the adjoint matrix of K. >> - Compute `r = 1/det(K) mod m`. >> - `K^(-1) = r*adj(K) mod m`. >> >> Examples >> ======== >> >> >>> A = Matrix(2, 2, [1, 2, 3, 4]) >> >>> print matrix_inverse_mod(A, 3) >> [ 8, -4] >> [-6, 2] >> >> """ >> from sympy import Matrix, gcd >> from sympy.ntheory import totient >> phi = totient(m) >> det_K = K.det() >> if gcd(det_K, m) != 1: >> raise ValueError('Matrix is not invertible (mod %d)'%m) >> det_inv = pow(det_K, phi-1, m) >> K_adj = K.cofactorMatrix().transpose() >> K_inv = det_inv*K_adj >> return K_inv >> >> Then you get >> >>>>> A = Matrix(2, 2, [1, 2, 3, 4]) >>>>> matrix_inverse_mod(A, 5) >> --------------------------------------------------------------------------- >> TypeError Traceback (most recent call last) >> ... >> --> 390 det_inv = pow(det_K, phi-1, m) >> ... >> TypeError: __sympifyit_wrapper() takes exactly 2 arguments (3 given) >> >> >> Does anyone know the source of this issue? >> >> - David >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sympy" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To post to this group, send email to [email protected]. >> Visit this group at http://groups.google.com/group/sympy?hl=en. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
