`nextpow2`

Exponent of the next power of two at or above abs(x).

Category: Mathematics > Elementary Math

Syntax

P = nextpow2(X)

Returns the smallest integer P such that 2^P >= abs(X).

Description

It is the ceiling of the base-2 logarithm of the magnitude, with exact powers of two returned exactly: nextpow2(1024) is 10 and nextpow2(1025) is 11. The classic use is padding a signal to a power-of-two length before an FFT: fft(x, 2^nextpow2(numel(x))).

Input arguments

X: Numeric array. Signs are ignored.

Output arguments

P: Array of integer-valued doubles. Values of X below 1 give zero or negative exponents.

Example

Padding length for an FFT

nextpow2([1 5 100 1000 1025])
n = 2^nextpow2(100)

Output

ans = 1×5

     0     3     7    10    11
n = 128

See also

log2 pow2 fft ceil