Integral Calculator in R
I Know How to Use Integral Calculator to Obtain Numeric Values, but Don't Know How to Get an Algebraic Equation. for Example: Integrand
I know how to use integral calculator to obtain numeric values, but don't know how to get an algebraic equation.
For example:
integrand <- function(x) {1/((x+1)*sqrt(x))}
integrate(integrand, lower = 0, upper = Inf)
with this code, I can get 3.141593 with absolute error < 2.7e-05
However, what if I want to use this code:
integrand <- function(x) {2*x}
integrate(integrand, lower = -Inf, upper = Inf)
to get x^2.
Apparently, it does not work.
If someone can help this, I would appreciate your help. Tons of thanks!
1 Answer
R doesn't do symbolic math but there are R packages that do. I will give (very) short examples using CRAN packages Ryacas and rSympy.
1. Package Ryacas.
library(Ryacas)
f <- ysym("2*x")
integrate(f, "x")
#y: x^2
2. Package rSymPy.
With package rSymPy you need to define the symbol "x" first. This is done with function Var.
Note: in my tests, the first time any of Var or sympy were called a series of warnings were given. I have interrupted R and at the second time all went well.
library(rSymPy)
x <- Var("x")
sympy("integrate(2*x)")
#[1] "x**2"
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