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sympy

Sympy - evalf vs subs

I don't get same results using evalf or using subs. Why?

from sympy import *

x = Symbol('x')
w = Symbol('w')
b = Symbol('b')
i = Symbol('I')
e = Symbol('E')
c3 = Symbol('c3')

m1 = w*b/2*x
yd1= integrate(-m1/e/i,x)
y1 = integrate(yd1,x)+c3
#yap = y1.evalf(subs={x:0})
yap = y1.subs(x,0)
print(yap)
c3sol = solve(yap,c3)[0]
y1 = y1.subs(c3,c3sol)
print(y1)

Using evalf it cannot find the correct solution.

Solution

  • evalf is used to evaluate to a number; indicating that x=0 does not reduce the expression to a number, so subs is the better choice here.