How to write and evaluate definite integrals (in Python, using SymPy)
Task
The area under a curve can be computed using a definite integral. To compute the area above the $x$ axis and under $f(x)$, from $x=a$ to $x=b$, we write
\[\int_a^b f(x)\;dx.\]How can we write and evaluate definite integrals using software?
Related tasks:
- How to compute the derivative of a function
- How to write and evaluate indefinite integrals
- How to write and evaluate Riemann sums
Solution
This answer assumes you have imported SymPy as follows.
1
2
from sympy import * # load all math functions
init_printing( use_latex='mathjax' ) # use pretty math output
Let’s compute the area under $\sin x$ from $x=0$ to $x=\pi$.
We use the same technique as in how to write and evaluate indefinite integrals, except that we add the lower and upper bounds together with $x$, as shown below.
1
2
3
var( 'x' )
formula = sin(x)
Integral( formula, (x,0,pi) )
$\displaystyle \int\limits_{0}^{\pi} \sin{\left(x \right)}\, dx$
The above code just displays the definite integral.
To evaluate it, use the integrate command.
1
integrate( formula, (x,0,pi) )
$\displaystyle 2$
Content last modified on 24 July 2023.
See a problem? Tell us or edit the source.
Contributed by Nathan Carter (ncarter@bentley.edu)