nextpow2

Exponent of next higher power of 2

Syntax

P = nextpow2(A)

Description

P = nextpow2(A) returns the exponents for the smallest powers of two that satisfy

$$2^p\ge \left|A\right|$$

for each element in A. By convention, nextpow2(0) returns zero.

You can use nextpow2 to pad the signal you pass to fft. Doing so can speed up the computation of the FFT when the signal length is not an exact power of 2.

Examples

Next Power of 2 of Double Integer Values

Define a vector of double integer values and calculate the exponents for the next power of 2 higher than those values.

a = [1 -2 3 -4 5 9 519];
p = nextpow2(a)

p = 1×7

     0     1     2     2     3     4    10

Calculate the positive next powers of 2.

np2 = 2.^p

np2 = 1×7

           1           2           4           4           8          16        1024

Preserve the sign of the original input values.

np2.*sign(a)

ans = 1×7

           1          -2           4          -4           8          16        1024

Next Power of 2 of Unsigned Integer Values

Define a vector of unsigned integers and calculate the exponents for the next power of 2 higher than those values.

a = uint32([1020 4000 32700]);
p = nextpow2(a)

p = 1x3 uint32 row vector

   10   12   15

Calculate the next powers of 2 higher than the values in a.

2.^p

ans = 1x3 uint32 row vector

    1024    4096   32768

Optimize FFT with Padding

Use the nextpow2 function to increase the performance of fft when the length of a signal is not a power of 2.

Create a 1-D vector containing 8191 sample values.

rng default;
x = rand([1,8191]);

Calculate the next power of 2 higher than 8191.

p = nextpow2(8191);
n = 2^p

n = 8192

Pass the signal and the next power of 2 to the fft function.

y = fft(x,n);

Input Arguments

A — Input values

scalar, vector, or array of real numbers

Input values, specified as a scalar, vector, or array of real numbers of any numeric type.

Example: 15

Example: [-15.123 32.456 63.111]

Example: int16([-15 32 63])

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Extended Capabilities

Tall Arrays

Calculate with arrays that have more rows than fit in memory.

This function fully supports tall arrays. For more information, see Tall Arrays.

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

This function fully supports GPU arrays. For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Distributed Arrays

Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).