# How to convert a list of polynomials into a list of equations and plug into Contourplot? [duplicate]

Given a list q of polynomials (output of GroebnerBasis) in two variables I want to transform the list into a list of equations and plug it into CountourPlot. For example

q = {y1^2 + y2^2 - 1, y1 - y2};
ContourPlot[{q[[1]] == 0, q[[2]] == 0}, {y1, -2, 2}, {y2, -2, 2}]
ContourPlot[Thread[Equal[q, 0]], {y1, -2, 2}, {y2, -2, 2}]


The second line works but is not suitable (unknown number of equations in general) and the third line produces an empty plot (although

    {q[[1]] == 0, q[[2]] == 0} == Thread[Equal[q, 0]]


evalutes True). Is there another way to plot level curves of an unknown list of polynomials ?

• In your last command, wrap your first argument in Evaluate. – Fred Simons Apr 23 '15 at 10:34
• @FredSimons has got it. When in doubt, add an Evaluate and see what happens. – Michael Seifert Apr 23 '15 at 13:47