1 | # Algebra (symbolic computation)
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2 |
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3 | math.js has built-in support for symbolic computation ([CAS](https://www.wikiwand.com/en/Computer_algebra_system)). It can parse expressions into an expression tree and do algebraic operations like simplification and derivation on the tree.
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4 |
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5 | > It's worth mentioning an excellent extension on math.js here: [mathsteps](https://github.com/socraticorg/mathsteps), a step-by-step math solver library that is focused on pedagogy (how best to teach). The math problems it focuses on are pre-algebra and algebra problems involving simplifying expressions.
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7 |
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8 | ## Simplify
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9 |
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10 | The function [`math.simplify`](../reference/functions/simplify.md) simplifies an expression tree:
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11 |
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12 | ```js
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13 | // simplify an expression
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14 | console.log(math.simplify('3 + 2 / 4').toString()) // '7 / 2'
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15 | console.log(math.simplify('2x + 3x').toString()) // '5 * x'
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16 | console.log(math.simplify('x^2 + x + 3 + x^2').toString()) // '2 * x ^ 2 + x + 3'
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17 | console.log(math.simplify('x * y * -x / (x ^ 2)').toString()) // '-y'
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18 | ```
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19 |
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20 | The function accepts either a string or an expression tree (`Node`) as input, and outputs a simplified expression tree (`Node`). This node tree can be transformed and evaluated as described in detail on the page [Expression trees](expression_trees.md).
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21 |
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22 | ```js
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23 | // work with an expression tree, evaluate results
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24 | const f = math.parse('2x + x')
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25 | const simplified = math.simplify(f)
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26 | console.log(simplified.toString()) // '3 * x'
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27 | console.log(simplified.evaluate({x: 4})) // 12
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28 | ```
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29 |
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30 | For more details on the theory of expression simplification, see:
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31 |
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32 | - [Strategies for simplifying math expressions (Stackoverflow)](https://stackoverflow.com/questions/7540227/strategies-for-simplifying-math-expressions)
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33 | - [Symbolic computation - Simplification (Wikipedia)](https://en.wikipedia.org/wiki/Symbolic_computation#Simplification)
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34 |
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35 |
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36 | ## Derivative
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37 |
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38 | The function [`math.derivative`](../reference/functions/derivative.md) finds the symbolic derivative of an expression:
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39 |
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40 | ```js
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41 | // calculate a derivative
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42 | console.log(math.derivative('2x^2 + 3x + 4', 'x').toString()) // '4 * x + 3'
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43 | console.log(math.derivative('sin(2x)', 'x').toString()) // '2 * cos(2 * x)'
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44 | ```
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45 |
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46 | Similar to the function `math.simplify`, `math.derivative` accepts either a string or an expression tree (`Node`) as input, and outputs a simplified expression tree (`Node`).
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47 |
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48 | ```js
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49 | // work with an expression tree, evaluate results
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50 | const h = math.parse('x^2 + x')
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51 | const x = math.parse('x')
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52 | const dh = math.derivative(h, x)
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53 | console.log(dh.toString()) // '2 * x + 1'
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54 | console.log(dh.evaluate({x: 3})) // '7'
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55 | ```
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56 |
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57 | The rules used by `math.derivative` can be found on Wikipedia:
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58 |
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59 | - [Differentiation rules (Wikipedia)](https://en.wikipedia.org/wiki/Differentiation_rules)
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60 |
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61 |
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62 | ## Rationalize
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63 |
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64 | The function [`math.transform`](../reference/functions/transform.md) transforms a rationalizable expression in a rational fraction.
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65 | If rational fraction is one variable polynomial then converts the numerator and denominator in canonical form, with decreasing exponents, returning the coefficients of numerator.
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66 |
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67 | ```js
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68 |
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69 | math.rationalize('2x/y - y/(x+1)')
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70 | // (2*x^2-y^2+2*x)/(x*y+y)
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71 | math.rationalize('(2x+1)^6')
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72 | // 64*x^6+192*x^5+240*x^4+160*x^3+60*x^2+12*x+1
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73 | math.rationalize('2x/( (2x-1) / (3x+2) ) - 5x/ ( (3x+4) / (2x^2-5) ) + 3')
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74 | // -20*x^4+28*x^3+104*x^2+6*x-12)/(6*x^2+5*x-4)
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75 |
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76 | math.rationalize('x+x+x+y',{y:1}) // 3*x+1
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77 | math.rationalize('x+x+x+y',{}) // 3*x+y
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78 |
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79 | const ret = math.rationalize('x+x+x+y',{},true)
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80 | // ret.expression=3*x+y, ret.variables = ["x","y"]
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81 | const ret = math.rationalize('-2+5x^2',{},true)
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82 | // ret.expression=5*x^2-2, ret.variables = ["x"], ret.coefficients=[-2,0,5]
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83 | ``` |
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