Calculus with Sympy

• Post by: Anurag Gupta
• October 9, 2021
• No Comment

Sympy is a python package through which we can perform calculus operations in mathematics like differentiation, integration, limits, infinite series, and so on. It is a python library used mainly for symbolic mathematics. The installation of this library is simple by using the following command:

pip install sympy

In order to write any symbolic expressions, firstly, we have to declare the symbolic variables that are involved in the symbolic expression. This can be done by:

• sympy.Symbol( ): used to declare a single variable by passing a variable as a string
• sympy.symbols( ): used to declare multi variables.
  
  1. Differentiation:
  Differentiation of any function can be done through the command diff(func, var,n) . Here, the “func” represents the symbolic function that is to be differentiated, “var” denotes the variable with respect to which we have to differentiate the function, and “n” denotes the nth derivative that needs to be computed for the function. This can be illustrated as:
  
  

# Importing essential library
import sympy as sym
 
# Declaration of the variables
x, y, z = sym.symbols('x y z')
 
# function whose derivative is to be find
f = x**5 * y - y**2 + z
 
# Differentiating f with respect to x
derivative_x = sym.diff(f, x, 2)
print('derivative w.r.t x: ',
      derivative_x)
 
# Differentiating exp with respect to y
derivative_y = sym.diff(f, y, 2)
print('derivative w.r.t y: ',
      derivative_y)

The output obtained is:

derivative w.r.t x:  20*x**3*y
derivative w.r.t y:  -2

2. Integration :

Through sympy, we can do both definite as well as indefinite integration by using integerate() function.

The general syntax used for the indefinite integration is given as:
sympy.integrate(func, var)

Here, “func” represents the function that is to be integrated and “var” represents the variable with respect to which it is integrated.

This can be illustrated as:

# Indefinite integration of sin(x) w.r.t. x
integration = sym.integrate(sym.sin(x), x)
print('indefinite integral of sin(x): ',
      integration)

The output obtained is:

indefinite integral of sin(x):  -cos(x)

The general syntax used for the definite integration is given as:
sympy.integrate(func, (var, lower_limit, upper_limit))

Here, lower_limit and upper_limit denote the lower and upper limit of the definite integration respectively.

This can be illustrated as:

# Definite integration of cos(x) w.r.t. x between -1 to 1
integration = sym.integrate(sym.cos(x), (x, -1, 1))
print('definite integral of cos(x) between -1 to 1: ',
      integration)

The output obtained is:

definite integral of cos(x) between -1 to 1:  2*sin(1)

In sympy, infinity (∞) is written as oo.

3. Limits:

The limit of a function can be computed using this library by using limit(function, variable, point).

This can be illustrated as:

# Calculating limit of f(x) = 1/x as x tends to ∞
limit_a = sym.limit(1/x, x, sym.oo)
print(limit_a)
# Calculating limit of f(x) = tan(x)/x as x tends to 0
limit_b = sym.limit(sym.tan(x)/x, x, 0)
print(limit_b)

The output obtained is:

0
1

4. Series expansion:

The Taylor series expansions of functions around a point can be computed using sympy library. In order to compute the series expansion of f(x) around the point, x=x₀ terms of order xⁿ, the syntax used is:

sympy.series(f, x, x0, n)

The default value of x₀=0 and n=6 is considered in case if they can be omitted from the syntax.

This can be illustrated as:

#  series expansion 
series = sym.series(sym.sin(x), x)
print(series)

The output obtained is:

x - x**3/6 + x**5/120 + O(x**6)