2016-07-20 09:06:30 +0100 commented answer Unable to create a contour_plot of a system of inequalities Thanks! It turns out the problem wasn't with what the function returned but with the inequalities. I set f1 < -1e-3, f2 < -1e-3, f3 < -1e-3 and it works how I wanted. This is a very strange bug that really makes sage a black box to me :( 2016-07-18 13:08:15 +0100 received badge ● Student (source) 2016-07-16 21:50:18 +0100 asked a question Unable to create a contour_plot of a system of inequalities I am trying to plot a system of inequalities, dependent on a matrix H. Here is my function I am planning to contour_plot: def reg(x, y): f1 = H[0,0] * H[0,0] * x + H[1,0] * H[1,0] * y f2 = H[0,0] * H[0,1] * x + H[1,0] * H[1,1] * y f3 = H[0,1] * H[0,1] * x + H[1,1] * H[1,1] * y if f1 < 0 or f2 < 0 or f3 < 0: return 0 else: return 1  I then have H be > H > [2.220446049250313e-16 -0.9999999999999998] > [ -0.9999999999999998 2.220446049250313e-16]  However contour_plot(reg, (x,-Integer(5),Integer(5)), (y,-Integer(5),Integer(5)))  yields an error. It says zero-size array to reduction operation minimum which has no identity  The strange part is that when > H > [-1 0] > [ 0 1]  the same contour_plot yields exactly what I want without any errors Help would be much appreciated, I have just picked up SAGE this week and have much to learn