trekhleb/javascript-algorithms · error · Error

Matrices have different dimensions

Error message

Matrices have different dimensions

What it means

Thrown by validateSameShape() in src/algorithms/math/matrix/Matrix.js:69 when the matrices passed to the element-wise operations add(), mul() or sub() have a different number of dimensions (rank). The library derives each matrix shape (e.g. [2,3] for 2 rows x 3 columns) and rejects the operation when the two shape arrays differ in length, because element-wise math is undefined across different nesting depths. Example: add([[1,2]], [[[1,2]]]) compares shape [1,2] against [1,1,2] and fails here. This is the rank check; per-axis size mismatches raise the separate 'Matrices have different shapes' error.

Source

Thrown at src/algorithms/math/matrix/Matrix.js:69

  }
};

/**
 * Validates that matrices are of the same shape.
 *
 * @param {Matrix} a
 * @param {Matrix} b
 * @trows {Error}
 */
export const validateSameShape = (a, b) => {
  validateType(a);
  validateType(b);

  const aShape = shape(a);
  const bShape = shape(b);

  if (aShape.length !== bShape.length) {
    throw new Error('Matrices have different dimensions');
  }

  while (aShape.length && bShape.length) {
    if (aShape.pop() !== bShape.pop()) {
      throw new Error('Matrices have different shapes');
    }
  }
};

/**
 * Generates the matrix of specific shape with specific values.
 *
 * @param {Shape} mShape - the shape of the matrix to generate
 * @param {function({CellIndex}): Cell} fill - cell values of a generated matrix.
 * @returns {Matrix}
 */
export const generate = (mShape, fill) => {
  /**

View on GitHub (pinned to 85293e3e2b)

Solutions

1. Print both shapes with the exported shape() helper (shape(a) vs shape(b)) to find which argument has the extra or missing nesting level
2. Fix the data: wrap the flat array ([1,2] becomes [[1,2]]) or flatten the deeper one so both matrices have the same rank
3. If you actually want matrix multiplication, call dot(a, b) instead of mul(a, b)
4. If per-axis sizes must be reconciled, pad or slice with zeros() until shapes match before calling add/mul/sub

Example fix

// before
import { add } from './src/algorithms/math/matrix/Matrix';
const result = add([[1, 2], [3, 4]], [1, 2]);
// throws: shapes [2,2] vs [2]

// after
const result = add([[1, 2], [3, 4]], [[1, 2], [1, 2]]);
// both shapes are [2,2]

import { shape } from './src/algorithms/math/matrix/Matrix';

const sameRank = (a, b) => shape(a).length === shape(b).length;
if (!sameRank(matrixA, matrixB)) {
  throw new TypeError('rank mismatch: ' + JSON.stringify(shape(matrixA)) + ' vs ' + JSON.stringify(shape(matrixB)));
}
const sum = add(matrixA, matrixB);

import { shape } from './src/algorithms/math/matrix/Matrix';

const isMatrixOfRank = (m, rank) => Array.isArray(m) && shape(m).length === rank;
// usage: isMatrixOfRank(a, 2) && isMatrixOfRank(b, 2)

try {
  result = add(a, b);
} catch (e) {
  if (e.message === 'Matrices have different dimensions') {
    throw new Error('add(): rank mismatch ' + JSON.stringify(shape(a)) + ' vs ' + JSON.stringify(shape(b)), { cause: e });
  }
  throw e;
}

When it happens

Trigger: Calling add(a, b), mul(a, b) or sub(a, b) where one argument is 2D ([[1,2],[3,4]]) and the other is 3D ([[[1,2]]]), or a flat row [1,2] is passed where a matrix [[1,2]] is expected (shape [2] vs [2,2]).

Common situations: Mixing data sources with different nesting conventions (flat points array vs grid), refactors that add or remove a nesting level, JSON round-trips that collapse single-element arrays, or passing a vector where the API expects a matrix.

Related errors

• Matrices have different shapes
• Matrices have incompatible shape for multiplication
• The method supports only positive integers

AI-assisted analysis of trekhleb/javascript-algorithms@85293e3e2b (2026-08-24). Data as JSON: /api/errors/b7509e0b7e8d0501. Report an issue: GitHub.