nextpow2 — Return the exponent p such that 2^p is the next power of two greater than or equal to abs(n).

nextpow2(X) applies the standard power-of-two exponent transform elementwise, returning ceil(log2(abs(X))) with zero mapped to zero. This is commonly used in FFT workflows such as 2^nextpow2(length(x)).

How nextpow2 works in RunMat

• nextpow2 accepts real numeric scalars and tensors.
• The transform is applied elementwise for array inputs.
• Zero maps to 0.
• Negative values use abs(X) before computing the exponent.
• Inf remains infinite and NaN remains NaN.
• GPU tensors use a unary provider hook when available and otherwise gather to the host.
• The output preserves the input's scalar/tensor shape.

Examples

Compute an FFT-friendly zero-padding length

x = rand(1000, 1);
N = 2^nextpow2(length(x))

Apply nextpow2 elementwise to an array

p = nextpow2([0 1 3 9])

Expected output:

p = [0 0 2 4]

FAQ

Why does nextpow2 return an exponent instead of the actual power of two?

That matches MATLAB semantics. To get the actual power of two, use 2^nextpow2(x) for a scalar or 2.^nextpow2(X) elementwise for arrays.

How is nextpow2 used in FFT workflows?

A common pattern is N = 2^nextpow2(length(x)), which computes a power-of-two transform length suitable for zero padding before an FFT.

Does nextpow2 preserve array shape?

Yes. The transform is elementwise and the output has the same scalar/tensor shape as the input.

Related functions to explore

These functions work well alongside nextpow2. Each page has runnable examples you can try in the browser.

fft, pow2, length

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