plus — Compute element-wise addition in MATLAB and RunMat.

plus(A, B) (or A + B) adds corresponding elements of A and B. Implicit expansion, complex handling, and output-shape behavior follow MATLAB semantics.

Syntax

C = plus(A, B)
C = plus(A, B, "like", prototype)

Inputs

Returns

Errors

How plus works

• Supports real, complex, logical, and character inputs; logical and character data are promoted to double precision before addition.
• Implicit expansion works across any dimension, provided the non-singleton extents match. Size mismatches raise the standard MATLAB-compatible error message.
• Complex operands follow MATLAB's analytic rule (a + ib) + (c + id) = (a + c) + i(b + d).
• Empty dimensions propagate naturally—if either operand has a zero-sized dimension after broadcasting, the result is empty with the broadcasted shape.
• Integer addition preserves the integer class. The other operand must use the same integer class or be scalar double; fractional results round, overflow saturates, and 64-bit integer/scalar-double arithmetic uses the extended-precision compatibility path.
• Sparse real matrices interoperate with sparse, dense, logical, character, scalar, and complex operands. Sparse-sparse addition preserves sparse storage; dense, nonzero scalar, and complex interop returns full real or complex storage when implicit zeros become nonzero.
• In RunMat compatibility mode, the RunMat-only optional 'like' prototype makes the output adopt the residency and complexity characteristics of the prototype. MATLAB-compatible mode rejects this extension before dispatch.

Does RunMat run plus on the GPU?

When a gpuArray provider is active:

1. If both operands are gpuArrays with identical shapes, RunMat dispatches to the provider's elem_add hook, including for complex-interleaved resident handles. 2. If one operand is a real scalar and the other is a gpuArray, the runtime calls scalar_add to keep the result on the device. 3. For shape-compatible implicit expansion, RunMat first expands gpuArray operands on device with repmat and then dispatches elem_add. 4. The fusion planner treats plus as a fusible elementwise node, so adjacent elementwise producers/consumers can execute inside a single WGSL kernel or provider-optimised pipeline, avoiding spurious host↔device transfers. 5. Unsupported shapes or operand kinds gather transparently to host memory, compute the result with full MATLAB semantics, and return a host tensor unless a 'like' GPU prototype is supplied—in which case the runtime re-uploads the output to honour the residency request.

GPU memory and residency

RunMat's auto-offload planner keeps tensors on the GPU whenever fused expressions benefit from device execution. Explicit gpuArray / gather calls remain supported for MATLAB code that manages residency manually. When the active provider lacks the kernels needed for a particular call (for example, implicit expansion between gpuArrays of different shapes), RunMat gathers back to the host, computes the MATLAB-accurate result, and resumes execution seamlessly.

Examples

Adding two matrices element-wise

A = [1 2 3; 4 5 6];
B = [7 8 9; 1 2 3];
S = plus(A, B)

Expected output:

S =
     8    10    12
     5     7     9

Adding a scalar to every element of a matrix

A = magic(3);
shifted = plus(A, 0.5)

Expected output:

shifted =
    8.5    1.5    6.5
    3.5    5.5    9.5
   10.5    7.5    2.5

Using implicit expansion between a column and row vector

col = (1:3)';
row = [10 20 30];
m = plus(col, row)

Expected output:

m =
    11    21    31
    12    22    32
    13    23    33

Adding complex inputs element-wise

z1 = [1+2i, 3-4i];
z2 = [2-1i, -1+1i];
sumz = plus(z1, z2)

Expected output:

sumz =
     3 + 1i     2 - 3i

Adding character codes to produce numeric arrays

letters = 'ABC';
codes = plus(letters, 2)

Expected output:

codes = [67 68 69]

Keeping element-wise sums on the GPU with 'like'

proto = gpuArray.zeros(1, 1);
G1 = gpuArray([1 2 3]);
G2 = gpuArray([4 5 6]);
deviceSum = plus(G1, G2, 'like', proto);
result = gather(deviceSum)

Expected output:

deviceSum =
  1x3 gpuArray
     5     7     9
result =
     5     7     9

Using plus with coding agents

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

FAQ

Related Math functions

Open-source implementation

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

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

About RunMat

RunMat is an open-source runtime that executes MATLAB-syntax code blazing on any GPU. It is licensed under the Apache 2.0 license.

• RunMat automatically optimizes your math for GPU execution on Apple, Nvidia, and AMD hardware. No code changes needed. Simulations that took hours now take minutes.
• Start running code in seconds. RunMat runs in the browser, on the desktop, or from the CLI. No license server, no IT ticket.

Getting started · Benchmarks · Pricing