Dear Volker Braun, Thanks so much that is what I need Thanks Doaa On 25 April 2012 14:05, Volker Braun <[email protected]> wrote: > Note that this is a question about convex polyhedra since it involves > inequalities! You can't solve it with linear algebra alone. A simple way is > to intersect your null space with the positive orthant, which gives you a > cone in your null space whose elements have all positive entries: > > sage: kernel = Polyhedron(lines=[ > ....: [ 1, 0, 1, 0, -1, 0, 0], > ....: [ 0, 1, 1, 0, 0, 0, 0], > ....: [ 0, 0, 0, 1, 1, 0, 0], > ....: [ 0, 0, 0, 0, 0, 1, 1]]) > sage: positive = Polyhedron(rays=identity_matrix(7).columns()) > sage: pos_ker = kernel.intersection(positive) > sage: pos_ker > A 4-dimensional polyhedron in ZZ^7 defined as the convex hull of 1 vertex > and 4 rays > sage: pos_ker.rays() > (A ray in the direction (0, 0, 0, 0, 0, 1, 1), A ray in the direction (0, 0, > 0, 1, 1, 0, 0), A ray in the direction (0, 1, 1, 0, 0, 0, 0), A ray in the > direction (1, 0, 1, 1, 0, 0, 0)) > > > > > On Tuesday, April 24, 2012 9:36:04 AM UTC-4, Doaa El-Sakout wrote: >> >> Hi >> >> I am using right_kernel to find a kernel, for example the result is >> [ 1 0 1 0 -1 0 0] >> [ 0 1 1 0 0 0 0] >> [ 0 0 0 1 1 0 0] >> [ 0 0 0 0 0 1 1] >> >> How can I (for an arbitrary kernel) get positive entries only, >> by making a linear combination of rows? >> >> Regards, >> Doaa > > -- > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/sage-support > URL: http://www.sagemath.org
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