gammaln — Compute the natural logarithm of the gamma function element-wise in MATLAB and RunMat.
Y = gammaln(A) evaluates log(gamma(A)) for real nonnegative inputs while avoiding the overflow that can occur when computing gamma(A) first.
Syntax
Y = gammaln(A)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
A | Any | Yes | — | Real nonnegative numeric input. |
Returns
| Name | Type | Description |
|---|---|---|
Y | NumericArray | Natural logarithm of the gamma function. |
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:gammaln:InvalidInput | Input cannot be interpreted as real, nonsparse numeric data. | gammaln: invalid input |
RunMat:gammaln:Domain | At least one real input value is negative. | gammaln: input must be nonnegative |
RunMat:gammaln:Internal | Internal tensor construction or provider interaction failed. | gammaln: internal error |
How gammaln works
gammaln(A)applies the log-gamma function element-by-element while preserving the input tensor shape.- Double inputs return double results; single tensors preserve single dtype metadata with single-rounded output values.
gammaln(0)returnsInf;gammaln(Inf)returnsInf;gammaln(NaN)returnsNaN.- Typed integer, logical, and character inputs are separate RunMat-only extensions and are rejected in strict compatibility mode.
- The integer extension admits all eight classes only when every value is exactly representable as binary64; output is double.
- Negative, complex, string, and sparse inputs produce stable typed errors.
- Real GPU tensors stay with their owning provider. Native output is validated for shape, precision, real storage, and ownership; all fallback results are restored to that owner.
GPU memory and residency
Yes for admitted gpuArray inputs. Documented floating inputs use validated native output when possible; host fallback and RunMat-only integer or logical extension paths upload the result back to the original owning provider.
Examples
Evaluate the log-gamma function at a scalar
y = gammaln(5)Expected output:
y = 3.1781Evaluate a half-integer input
y = gammaln(0.5)Expected output:
y = 0.5724Apply gammaln element-wise to an array
A = [0.5 1 2 5];
Y = gammaln(A)Expected output:
Y = [0.5724 0 0 3.1781]Avoid gamma overflow for large inputs
y = gammaln(171)Expected output:
y = 706.5731Run gammaln on GPU data
G = gpuArray([0.5 1 5]);
out = gammaln(G);
result = gather(out)Expected output:
result = [0.5724 0 3.1781]Using gammaln with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how gammaln changes the result.
Run a small gammaln example, explain the result, then change one input and compare the output.
FAQ
Why use gammaln(A) instead of log(gamma(A))?⌄
gammaln evaluates the logarithm directly, so large positive inputs can remain finite even when gamma(A) would overflow before the logarithm is taken.
Does gammaln support complex or negative inputs?⌄
No. MATLAB documents gammaln for real nonnegative input, and RunMat reports typed errors for complex and negative values.
Can gammaln run on GPU arrays?⌄
Yes for real nonnegative single or double tensors. A valid native result stays resident; otherwise RunMat gathers, computes, and uploads the precision-preserving result back to the input's owning provider.
Related Math functions
Elementwise
abs · angle · bsxfun · complex · conj · double · erf · erfcinv · exp · expm1 · factorial · flintmax · gamma · heaviside · hypot · idivide · imag · intmax · intmin · ldivide · log · log10 · log1p · log2 · minus · nextpow2 · plus · pow2 · power · rdivide · real · realmax · realmin · realsqrt · rescale · sign · single · sqrt · swapbytes · times · typecast · uint16 · uint32 · uint8
Trigonometry
acos · acosh · asin · asinh · atan · atan2 · atanh · cos · cosd · cosh · cospi · deg2rad · pol2cart · rad2deg · sin · sind · sinh · sinpi · tan · tand · tanh
Reduction
all · any · bounds · cummax · cummin · cumprod · cumsum · cumtrapz · diff · gradient · max · maxk · mean · median · min · mink · movmax · movmean · movmedian · movmin · movprod · movstd · movsum · movvar · nnz · prod · rms · std · sum · trapz · var
Structure
bandwidth · isdiag · ishermitian · issymmetric · istril · istriu · symrcm
Signal
blackman · butter · buttord · cheb2ord · conv · conv2 · deconv · downsample · envelope · filter · filtfilt · fir1 · freqz · gauspuls · hamming · hann · hilbert · periodogram · pulstran · pwelch · rectpuls · resample · sawtooth · sinc · spectrogram · square · tripuls · unwrap · upsample · zplane
Optim
coneprog · fminbnd · fminunc · fsolve · fzero · integral · linprog · lsqcurvefit · lsqnonlin · optimoptions · optimset · quad · secondordercone
Ops
cross · ctranspose · dot · mldivide · mpower · mrdivide · mtimes · pagemtimes · pagetranspose · trace · transpose
About RunMat
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