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2, 3], [2, 4, 5], [6, 8, 9]], [1, 2, 3]))","expected_output":"[14, 25, 49]"},{"test":"print(matrix_dot_vector([[1, 2], [2, 4], [6, 8], [12, 4]], [1, 2, 3]))","expected_output":"-1"}],"pytorch_difficulty":"easy","likes":"0","video":"https://youtu.be/DNoLs5tTGAw?si=vpkPobZMA8YY10WY","cuda_test_cases":[{"test":"#include \n#include \n\nstd::vector matrix_dot_vector(const std::vector>& matrix, const std::vector& vec);\n\nint main() {\n std::vector> matrix = {{1, 2, 3}, {2, 4, 5}, {6, 8, 9}};\n std::vector vec = {1, 2, 3};\n auto result = matrix_dot_vector(matrix, vec);\n std::cout << \"[\";\n for (int i = 0; i < result.size(); i++) {\n std::cout << result[i];\n if (i < result.size() - 1) std::cout << \", \";\n }\n std::cout << \"]\" << std::endl;\n return 0;\n}","expected_output":"[14, 25, 49]"},{"test":"#include \n#include \n\nstd::vector matrix_dot_vector(const std::vector>& matrix, const std::vector& vec);\n\nint main() {\n std::vector> matrix = {{1, 2}, {2, 4}, {6, 8}, {12, 4}};\n std::vector vec = {1, 2, 3};\n auto result = matrix_dot_vector(matrix, vec);\n std::cout << result[0] << std::endl;\n return 0;\n}","expected_output":"-1"},{"test":"#include \n#include \n\nstd::vector matrix_dot_vector(const std::vector>& matrix, const std::vector& vec);\n\nint main() {\n std::vector> matrix = {{1.5f, 2.5f}, {3.0f, 4.0f}};\n std::vector vec = {2, 1};\n auto result = matrix_dot_vector(matrix, vec);\n std::cout << \"[\" << result[0] << \", \" << result[1] << \"]\" << std::endl;\n return 0;\n}","expected_output":"[5.5, 10]"}],"example":{"input":"a = [[1, 2], [2, 4]], b = [1, 2]","output":"[5, 10]","reasoning":"Row 1: (1 * 1) + (2 * 2) = 1 + 4 = 5; Row 2: (2 * 1) + (4 * 2) = 2 + 8 = 10"},"pytorch_starter_code":"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","learn_section":"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","cuda_starter_code":"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","contributor":[{"profile_link":"https://github.com/moe18","name":"Moe Chabot"}],"tinygrad_test_cases":[{"test":"from tinygrad.tensor import Tensor\nres = matrix_dot_vector_tg(\n Tensor([[1,2,3],[2,4,5],[6,8,9]]),\n Tensor([1,2,3])\n)\nprint(res.numpy().tolist())","expected_output":"[14.0, 25.0, 49.0]"},{"test":"from tinygrad.tensor import Tensor\nres = matrix_dot_vector_tg(\n Tensor([[1,2,3],[2,4,5]]),\n Tensor([1,2])\n)\nprint(res.item())","expected_output":"-1"},{"test":"from tinygrad.tensor import Tensor\nres = matrix_dot_vector_tg(\n Tensor([[1, 2], [2, 4]]),\n Tensor([1, 2])\n)\nprint(res.numpy().tolist())","expected_output":"[5.0, 10.0]"}],"description":"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","id":"1","tinygrad_difficulty":"easy","playground":{"dependencies":{},"enabled":true,"type":"react","settings":{"editorHeight":600,"showPreview":true,"theme":"dark","showEditor":false,"editorWidthPercentage":35,"showConsole":false},"files":{"/App.js":{"active":true,"code":"import React, { useState, useMemo } from 'react';\n\n// ============================================\n// Inline SVG Icons (replaces lucide-react)\n// ============================================\nconst Icons = {\n Grid3X3: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n ArrowRight: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n X: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n Check: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n AlertCircle: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n Play: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n RotateCcw: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n ChevronDown: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n ChevronUp: ({ size = 24, color = 'currentColor' }) => (\n \n \n \n ),\n};\n\n// ============================================\n// Design Tokens\n// ============================================\nconst theme = {\n colors: {\n primary: '#6366f1',\n primaryHover: '#4f46e5',\n secondary: '#ffffff',\n background: '#000000',\n surface: '#0a0a0a',\n surfaceAlt: '#111111',\n border: '#1f1f1f',\n borderLight: '#2a2a2a',\n text: '#ffffff',\n textSecondary: '#a1a1aa',\n textMuted: '#71717a',\n success: '#22c55e',\n error: '#ef4444',\n highlight: '#6366f1',\n },\n font: \"'JetBrains Mono', monospace\",\n};\n\n// ============================================\n// Card Component\n// ============================================\nfunction Card({ children, className = '' }) {\n return (\n \n {children}\n \n );\n}\n\n// ============================================\n// Matrix Cell\n// ============================================\nfunction MatrixCell({ value, onChange, highlighted, highlightColor, editable = true }) {\n return (\n onChange(parseFloat(e.target.value) || 0)}\n disabled={!editable}\n style={{\n width: '48px',\n height: '48px',\n background: highlighted ? `${highlightColor}20` : theme.colors.surfaceAlt,\n border: `2px solid ${highlighted ? highlightColor : theme.colors.border}`,\n borderRadius: '8px',\n color: highlighted ? highlightColor : theme.colors.text,\n fontFamily: theme.font,\n fontSize: '16px',\n fontWeight: '600',\n textAlign: 'center',\n outline: 'none',\n transition: 'all 0.2s ease',\n }}\n />\n );\n}\n\n// ============================================\n// Vector Cell\n// ============================================\nfunction VectorCell({ value, onChange, highlighted, highlightColor, editable = true }) {\n return (\n onChange(parseFloat(e.target.value) || 0)}\n disabled={!editable}\n style={{\n width: '48px',\n height: '48px',\n background: highlighted ? `${highlightColor}20` : theme.colors.surfaceAlt,\n border: `2px solid ${highlighted ? highlightColor : theme.colors.border}`,\n borderRadius: '8px',\n color: highlighted ? highlightColor : theme.colors.text,\n fontFamily: theme.font,\n fontSize: '16px',\n fontWeight: '600',\n textAlign: 'center',\n outline: 'none',\n transition: 'all 0.2s ease',\n }}\n />\n );\n}\n\n// ============================================\n// Result Bar\n// ============================================\nfunction ResultBar({ value, maxValue, index, highlighted }) {\n const percentage = Math.min(Math.abs(value) / maxValue * 100, 100);\n const isNegative = value < 0;\n \n return (\n
\n \n {index + 1}\n
\n
\n \n \n \n
\n \n \n {value.toFixed(1)}\n \n \n );\n}\n\n// ============================================\n// Calculation Step\n// ============================================\nfunction CalculationStep({ row, vector, rowIndex, isActive }) {\n const products = row.map((val, i) => val * vector[i]);\n const sum = products.reduce((a, b) => a + b, 0);\n \n if (!isActive) return null;\n \n return (\n \n
\n Row {rowIndex + 1} Calculation\n
\n \n
\n {row.map((val, i) => (\n \n {i > 0 && +}\n \n ({val}\n × \n {vector[i]})\n \n \n ))}\n =\n {products.map((p, i) => (\n \n {i > 0 && +}\n {p}\n \n ))}\n =\n \n {sum}\n \n
\n \n );\n}\n\n// ============================================\n// Main Component\n// ============================================\nexport default function MatrixVectorDot() {\n const [matrix, setMatrix] = useState([\n [1, 2, 3],\n [4, 5, 6],\n [7, 8, 9],\n ]);\n const [vector, setVector] = useState([1, 2, 3]);\n const [activeRow, setActiveRow] = useState(null);\n const [isAnimating, setIsAnimating] = useState(false);\n const [showSteps, setShowSteps] = useState(false);\n \n const rows = matrix.length;\n const cols = matrix[0].length;\n const vectorLen = vector.length;\n const isValid = cols === vectorLen;\n \n const result = useMemo(() => {\n if (!isValid) return null;\n return matrix.map(row => \n row.reduce((sum, val, i) => sum + val * vector[i], 0)\n );\n }, [matrix, vector, isValid]);\n \n const maxResult = result ? Math.max(...result.map(Math.abs), 1) : 1;\n \n const updateMatrix = (rowIdx, colIdx, value) => {\n const newMatrix = matrix.map((row, r) =>\n row.map((cell, c) => (r === rowIdx && c === colIdx ? value : cell))\n );\n setMatrix(newMatrix);\n };\n \n const updateVector = (idx, value) => {\n const newVector = vector.map((v, i) => (i === idx ? value : v));\n setVector(newVector);\n };\n \n const addRow = () => setMatrix([...matrix, Array(cols).fill(0)]);\n const removeRow = () => rows > 1 && setMatrix(matrix.slice(0, -1));\n const addCol = () => {\n setMatrix(matrix.map(row => [...row, 0]));\n setVector([...vector, 0]);\n };\n const removeCol = () => {\n if (cols > 1) {\n setMatrix(matrix.map(row => row.slice(0, -1)));\n setVector(vector.slice(0, -1));\n }\n };\n \n const animate = async () => {\n setIsAnimating(true);\n setShowSteps(true);\n for (let i = 0; i < rows; i++) {\n setActiveRow(i);\n await new Promise(r => setTimeout(r, 800));\n }\n setActiveRow(null);\n setIsAnimating(false);\n };\n \n const reset = () => {\n setMatrix([[1, 2, 3], [4, 5, 6], [7, 8, 9]]);\n setVector([1, 2, 3]);\n setActiveRow(null);\n setShowSteps(false);\n };\n\n return (\n \n
\n {/* Header */}\n
\n
\n \n

\n Matrix-Vector Dot Product\n

\n
\n

\n Each row of the matrix is dotted with the vector to produce a result\n

\n
\n \n {/* Dimension Controls */}\n \n
\n
\n Dimensions\n
\n
\n
\n Matrix: {rows} × {cols}\n
\n
\n Vector: {vectorLen}\n
\n
\n
\n \n
\n {[\n { label: '+ Row', action: addRow },\n { label: '- Row', action: removeRow },\n { label: '+ Col', action: addCol },\n { label: '- Col', action: removeCol },\n ].map(({ label, action }) => (\n {\n e.target.style.background = theme.colors.borderLight;\n e.target.style.color = theme.colors.text;\n }}\n onMouseLeave={(e) => {\n e.target.style.background = theme.colors.surfaceAlt;\n e.target.style.color = theme.colors.textSecondary;\n }}\n >\n {label}\n \n ))}\n
\n \n \n {/* Main Visualization */}\n \n {/* Validity Status */}\n \n {isValid ? (\n \n ) : (\n \n )}\n \n {isValid \n ? `Valid: ${cols} columns = ${vectorLen} vector length`\n : `Invalid: ${cols} columns ≠ ${vectorLen} vector length`\n }\n \n
\n \n {/* Matrix × Vector = Result */}\n
\n {/* Matrix */}\n
\n
\n Matrix A\n
\n \n {matrix.map((row, rowIdx) => (\n
\n {row.map((cell, colIdx) => (\n updateMatrix(rowIdx, colIdx, v)}\n highlighted={activeRow === rowIdx}\n highlightColor={theme.colors.primary}\n />\n ))}\n
\n ))}\n
\n
\n \n {/* Multiply Icon */}\n \n \n {/* Vector */}\n
\n
\n Vector b\n
\n \n {vector.map((val, idx) => (\n updateVector(idx, v)}\n highlighted={activeRow !== null}\n highlightColor={theme.colors.success}\n />\n ))}\n
\n \n \n {/* Equals */}\n \n \n {/* Result */}\n
\n
\n Result\n
\n \n {isValid && result ? (\n result.map((val, idx) => (\n \n {val}\n
\n ))\n ) : (\n \n -1\n \n )}\n \n \n \n \n {/* Calculation Steps */}\n {showSteps && isValid && (\n
\n {matrix.map((row, idx) => (\n \n ))}\n
\n )}\n \n {/* Controls - moved here, closer to animation */}\n
\n \n \n {isAnimating ? 'Animating...' : 'Animate Steps'}\n \n \n setShowSteps(!showSteps)}\n disabled={!isValid}\n style={{\n display: 'flex',\n alignItems: 'center',\n justifyContent: 'center',\n gap: '8px',\n padding: '14px 24px',\n background: theme.colors.surfaceAlt,\n border: `1px solid ${theme.colors.border}`,\n borderRadius: '8px',\n color: theme.colors.textSecondary,\n fontFamily: theme.font,\n fontSize: '14px',\n fontWeight: '500',\n cursor: isValid ? 'pointer' : 'not-allowed',\n }}\n >\n {showSteps ? : }\n {showSteps ? 'Hide' : 'Show'} Math\n \n \n \n \n Reset\n \n
\n \n \n {/* Result Bars */}\n {isValid && result && (\n \n
\n Result Visualization\n
\n
\n {result.map((val, idx) => (\n \n ))}\n
\n \n )}\n \n {/* Code Output */}\n \n
\n Python Output\n
\n \n \n # Input\n {'\\n'}\n matrix_dot_vector\n (\n {'\\n'}\n {JSON.stringify(matrix)},\n {'\\n'}\n {JSON.stringify(vector)}\n {'\\n'}\n )\n {'\\n\\n'}\n # Output\n {'\\n'}\n \n {isValid ? JSON.stringify(result) : '-1'}\n \n \n \n \n \n \n );\n}"}}},"difficulty":"easy","cuda_difficulty":"medium","dislikes":"0","category":"Linear Algebra","starter_code":"def matrix_dot_vector(a: list[list[int|float]], b: list[int|float]) -> list[int|float]:\n\t# Return a list where each element is the dot product of a row of 'a' with 'b'.\n\t# If the number of columns in 'a' does not match the length of 'b', return -1.\n\tpass","title":"Matrix-Vector Dot Product","createdAt":"July 22, 2026 at 9:04:06 AM UTUTC-4","pytorch_test_cases":[{"test":"import torch\nres = matrix_dot_vector(\n torch.tensor([[1,2,3],[2,4,5],[6,8,9]], dtype=torch.float),\n torch.tensor([1,2,3], dtype=torch.float)\n)\nprint(res.numpy().tolist())","expected_output":"[14.0, 25.0, 49.0]"},{"test":"import torch\nres = matrix_dot_vector(\n torch.tensor([[1,2,3],[2,4,5]], dtype=torch.float),\n torch.tensor([1,2], dtype=torch.float)\n)\nprint(res.item())","expected_output":"-1"}]}