mod — Compute modulus values with MATLAB semantics in RunMat.

C = mod(A, B) computes remainders using the MATLAB definition A - B .* floor(A./B). Sign conventions, broadcasting, and complex-value behavior follow MATLAB semantics.

Syntax

R = mod(A, B)

Inputs

Returns

Errors

How mod works

• Works with MATLAB-style implicit expansion (broadcasting) between A and B.
• Returns NaN for elements where B is zero or both arguments are non-finite in incompatible ways (Inf modulo finite, NaN inputs, etc.).
• Logical and integer inputs are promoted to double precision; character arrays operate on their Unicode code points.
• Complex inputs use the MATLAB definition mod(a, b) = a - b.*floor(a./b) with complex division and component-wise floor.
• Empty arrays propagate emptiness while retaining their shapes.

Does RunMat run mod on the GPU?

When both operands are GPU tensors with the same shape, RunMat composes mod from the provider hooks elem_div, unary_floor, elem_mul, and elem_sub. This keeps the computation on the device when those hooks are implemented (the shipped WGPU backend and in-process provider expose them). For mixed residency, shape-mismatched operands, or providers that lack any of these hooks, RunMat gathers to the host, applies the CPU implementation, and returns a host-resident result.

GPU memory and residency

Usually not. When the provider exposes the elementwise hooks noted above, mod executes entirely on the GPU. Otherwise RunMat gathers transparently, ensuring MATLAB-compatible behaviour without manual intervention. Explicit gpuArray / gather calls remain available for scripts that mirror MathWorks MATLAB workflows.

Examples

Computing the modulus of positive integers

r = mod(17, 5)

Expected output:

r = 2

Modulus with negative divisors keeps the divisor's sign

values = [-7 -3 4 9];
mods   = mod(values, -4)

Expected output:

mods = [-3 -3 0 -3]

Broadcasting a scalar divisor across a matrix

A = [4.5  7.1; -2.3  0.4];
result = mod(A, 2)

Expected output:

result =
    [0.5  1.1;
     1.7  0.4]

MATLAB-compatible modulus for complex numbers

z = [3 + 4i, -2 + 5i];
div = 2 + 1i;
res = mod(z, div)

Expected output:

res =
    [0.0 + 0.0i, 0.0 + 1.0i]

Handling zeros in the divisor

warn = mod([2, 0, -2], [0, 0, 0])

Expected output:

warn = [NaN NaN NaN]

Using mod with character arrays

letters = mod('ABC', 5)

Expected output:

letters = [0 1 2]

Staying on the GPU when hooks are available

G = gpuArray(-5:5);
H = mod(G, 4);
cpuCopy = gather(H)

Expected output:

cpuCopy = [3 0 1 2 3 0 1 2 3 0 1]

Using mod with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how mod changes the result.

FAQ

Related Math functions

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how mod is executed, line by line, in Rust.

• View the source for mod in Rust on GitHub
• Learn how the RunMat runtime works
• Found a bug? Open an issue with a minimal reproduction.

About RunMat

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