CODEWITHSUNDEEP
matrixsympyequationsolver
Yasha Berchenko-Kogan
Yasha Berchenko-Kogan

Reputation: 147

sympy nsolve with MatrixSymbol

I'd like to numerically solve an equation involving a MatrixSymbol. Here's a basic example:

import sympy as sy
v = sy.MatrixSymbol('v', 2, 1)
equation = (v - sy.Matrix([17, 23])).as_explicit()

I'd like something like:

sy.nsolve(equation, v, sy.Matrix([0,0]))

But because nsolve does not accept MatrixSymbols, I've made a cludgy workaround that gives the correct output of Matrix([[17.0], [23.0]]):

vx, vy = sy.symbols('v_x v_y')
sy.nsolve(equation.subs(v, sy.Matrix([vx, vy])), [vx, vy], [0,0])

Essentially, I've converted a MatrixSymbol to a matrix of Symbols to make nsolve happy.

Is there a better way I should be doing this?

Edit: the workaround can be simplified to:

vseq = sy.symbols('a b') #names must be distinct
sy.nsolve(equation.subs(v, sy.Matrix(vseq)), vseq, [0,0])

But there ought to be a cleaner way to convert a MatrixSymbol to a sequence of Symbols, or a way to avoid needing to do so in the first place.

Upvotes: 1

Views: 331

Answers (1)

user6655984
user6655984

Reputation:

A cleaner way is to create a Matrix from symarray:

v = sy.Matrix(sy.symarray("v", (2,)))
equation = v - sy.Matrix([17, 23])
sy.nsolve(equation, v, [0, 0])

Here, symarray creates a (NumPy) array of symbols [v_0, v_1] which is then turned into a Matrix. One can also use sy.symarray("v", (2, 1)) so it's a double array, but since SymPy's Matrix constructor is cool with 1D inputs, this is not necessary.

Upvotes: 1

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