erfi

Imaginary error function

Syntax

erfi(x)

Description

erfi(x) returns the imaginary error function of x. If x is a vector or a matrix, erfi(x) returns the imaginary error function of each element of x.

Examples

Imaginary Error Function for Floating-Point and Symbolic Numbers

Depending on its arguments, erfi can return floating-point or exact symbolic results.

Compute the imaginary error function for these numbers. Because these numbers are not symbolic objects, you get floating-point results.

s = [erfi(1/2), erfi(1.41), erfi(sqrt(2))]

s =
    0.6150    3.7382    3.7731

Compute the imaginary error function for the same numbers converted to symbolic objects. For most symbolic (exact) numbers, erfi returns unresolved symbolic calls.

s = [erfi(sym(1/2)), erfi(sym(1.41)), erfi(sqrt(sym(2)))]

s =
[ erfi(1/2), erfi(141/100), erfi(2^(1/2))]

Use vpa to approximate this result with the 10-digit accuracy:

vpa(s, 10)

ans =
[ 0.6149520947, 3.738199581, 3.773122512]

Imaginary Error Function for Variables and Expressions

Compute the imaginary error function for x and sin(x) + x*exp(x). For most symbolic variables and expressions, erfi returns unresolved symbolic calls.

syms x
f = sin(x) + x*exp(x);
erfi(x)
erfi(f)

ans =
erfi(x)
 
ans =
erfi(sin(x) + x*exp(x))

Imaginary Error Function for Vectors and Matrices

If the input argument is a vector or a matrix, erfi returns the imaginary error function for each element of that vector or matrix.

Compute the imaginary error function for elements of matrix M and vector V:

M = sym([0 inf; 1/3 -inf]);
V = sym([1; -i*inf]);
erfi(M)
erfi(V)

ans =
[         0,  Inf]
[ erfi(1/3), -Inf]
 
ans =
 erfi(1)
      -1i

Special Values of Imaginary Error Function

Compute the imaginary error function for x = 0, x = ∞, and x = –∞. Use sym to convert 0 and infinities to symbolic objects. The imaginary error function has special values for these parameters:

[erfi(sym(0)), erfi(sym(inf)), erfi(sym(-inf))]

ans =
[ 0, Inf, -Inf]

Compute the imaginary error function for complex infinities. Use sym to convert complex infinities to symbolic objects:

[erfi(sym(i*inf)), erfi(sym(-i*inf))]

ans =
[ 1i, -1i]

Handling Expressions That Contain Imaginary Error Function

Many functions, such as diff and int, can handle expressions containing erfi.

Compute the first and second derivatives of the imaginary error function:

syms x
diff(erfi(x), x)
diff(erfi(x), x, 2)

ans =
(2*exp(x^2))/pi^(1/2)
 
ans =
(4*x*exp(x^2))/pi^(1/2)

Compute the integrals of these expressions:

int(erfi(x), x)
int(erfi(log(x)), x)

ans =
x*erfi(x) - exp(x^2)/pi^(1/2)
 
ans =
x*erfi(log(x)) - int((2*exp(log(x)^2))/pi^(1/2), x)

Plot Imaginary Error Function

Plot the imaginary error function on the interval from -2 to 2.

syms x
fplot(erfi(x),[-2,2])
grid on

Input Arguments

x — Input

floating-point number | symbolic number | symbolic variable | symbolic expression | symbolic function | symbolic vector | symbolic matrix

Input, specified as a floating-point or symbolic number, variable, expression, function, vector, or matrix.

More About

Imaginary Error Function

The imaginary error function is defined as:

$$erfi\left(x\right)=-ierf\left(ix\right)=\frac{2}{\sqrt{\pi }}{\displaystyle \underset{0}{\overset{x}{\int }}{e}^{t^2}dt}$$

Tips

• erfi returns special values for these parameters:

  • erfi(0) = 0

  • erfi(inf) = inf

  • erfi(-inf) = -inf

  • erfi(i*inf) = i

  • erfi(-i*inf) = -i

Version History

Introduced in R2013a