Python sympy.subs() method

sympy.subs() method in Python is used to substitute a variable or expression with a specified value or another expression in a symbolic mathematical expression. It is part of the SymPy library, which provides functionality for symbolic mathematics in Python, allowing you to work with equations, polynomials, integrals, and more.

Example: Basic Variable Substitution Using sympy.subs()

This example demonstrates how to substitute one variable with another symbolic variable in an expression.

Output

Before Substitution : x**2 + 1
After Substitution : y**2 + 1

Explanation:

The code uses SymPy to create symbolic variables x and y. The expression x**2 + 1 is defined. The subs() method is used to replace x with y in the expression.

• Initially, the expression is x**2 + 1.
• After substitution, x is replaced by y, resulting in the expression y**2 + 1.

Syntax

sympy.subs(old, new)

Parameters

• old: The variable or expression to be replaced.
• new: The value or expression that will replace the old variable or expression.

Return Value

The method returns a new expression with the substitution made. It does not modify the original expression but returns a new expression where the substitution is applied.

Examples of sympy.subs() method

1. Substitute with a Numeric Value Using sympy.subs()

This example shows how to substitute a variable with a numeric value (0 in this case) in a mathematical expression.

Output

Before Substitution : cos(x) + 7
After Substitution : 8

Explanation:

• x = symbols('x'): Creates a symbolic variable x.
• exp = cos(x) + 7: Creates an expression cos(x) + 7 using the symbolic variable x.
• exp.subs(x, 0): Substitutes x with 0 in the expression cos(x) + 7.

2. Multiple Variable Substitution Using sympy.subs()

This example illustrates how to perform multiple variable substitutions simultaneously using a list of tuples in the subs() method.

Output

Before Substitution : x**2 + 7*y + z
After Substitution : 33

Explanation: The code defines the symbolic variables x, y, and z using SymPy. It then creates an expression x**2 + 7 * y + z, and substitutes values for x, y, and z using the subs() method.