# isinf

Check whether symbolic array elements are infinite

## Syntax

``isinf(A)``

## Description

example

````isinf(A)` returns an array of the same size as `A` containing logical `1`s (true) where the elements of `A` are infinite, and logical `0`s (false) where they are not. For a complex number, `isinf` returns `1` if the real or imaginary part of that number is infinite or both real and imaginary parts are infinite. Otherwise, it returns `0`.```

## Examples

### Determine Which Elements of Symbolic Array Are Infinite

Using `isinf`, determine which elements of this symbolic matrix are infinities:

`isinf(sym([pi NaN Inf; 1 + i Inf + i NaN + i]))`
```ans = 2×3 logical array 0 0 1 0 1 0```

### Determine if Exact and Approximated Values Are Infinite

Approximate these symbolic values with the 50-digit accuracy:

```V = sym([pi, 2*pi, 3*pi, 4*pi]); V_approx = vpa(V, 50);```

The cotangents of the exact values are infinite:

```cot(V) isinf(cot(V))```
```ans = [ Inf, Inf, Inf, Inf] ans = 1×4 logical array 1 1 1 1```

Nevertheless, the cotangents of the approximated values are not infinite due to the round-off errors:

`isinf(cot(V_approx))`
```ans = 1×4 logical array 0 0 0 0```

## Input Arguments

collapse all

Input value, specified as a symbolic number, variable, expression, or function, or as an array, vector, or matrix of symbolic numbers, variables, expressions, functions.

## Tips

• For any `A`, exactly one of the three quantities `isfinite(A)`, `isinf(A)`, or `isnan(A)` is `1` for each element.

• The elements of `A` are recognized as infinite if they are

• Symbolic `Inf` or `-Inf`

• Sums or products containing symbolic `Inf` or `-Inf` and not containing the value `NaN`.