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#76 - Better break-up fraction. #158

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#76 - Better break-up fraction. #158

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aee08a1
Issue #76 - Better break-up fraction.
eltonlaw Apr 21, 2017
6135dad
add check for denonimator in numerator
eltonlaw Apr 21, 2017
322a247
Issue #76 - Better break-up fraction
eltonlaw May 4, 2017
3c1cac0
lint
eltonlaw May 4, 2017
1ccdc3b
added test cases, checks are more rigorous
eltonlaw May 15, 2017
a46849d
Merge branch 'master' into master
eltonlaw May 15, 2017
fd8ebf0
add comments
eltonlaw May 15, 2017
f779651
update
eltonlaw May 16, 2017
41e9223
squash line 55-56 into one if statement
eltonlaw May 16, 2017
308a90c
Add changes
eltonlaw May 21, 2017
d88605f
Add TODO's
eltonlaw May 27, 2017
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61 changes: 61 additions & 0 deletions lib/checks/canFindDenominatorInNumerator.js
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@@ -0,0 +1,61 @@
const Node = require('../node');

// Returns true if by adding a term you can simplify part of the function into
// an integer
// e.g. (2x+1)/(2x+3) -> True because of the following simplification
// (2x+1)/(2x+3) -> (2x + 3)/(2x + 3) - 2/(2x + 3) -> 1 - 2/(2x + 3)
// e.g. (2x+1)/(2x^2 + 3) -> False
function canFindDenominatorInNumerator(node) {
if (!Node.Type.isOperator(node) || node.op !== '/' ) {
return false;
}
if (node.args.length !== 2) {
return false;
}
let numerator = node.args[0];
let denominator = node.args[1];
if (Node.Type.isParenthesis(numerator)) {
numerator = numerator.content;
}
if (Node.Type.isParenthesis(denominator)) {
denominator = denominator.content;
}
if (!(numerator.op === '+' || numerator.op === '-' ||
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can you add a comment explaining why you check for these things and why these are the only conditions that make us keep going?

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Okay

denominator.op === '+' || numerator.op === '-')) {
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why do you have numerator.op === '-' twice?

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whoops that should be denominator.op

return false;
}
if (denominator.op !== '+') {
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why do you have this condition? what about (2x + 2) / 2x

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I was thinking we don't need to use this extended version on it. The original breakUpNumerator function works fine for this case. But I think you've highlighted an interesting point, anyone reading the code would be confused.

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ooo true. Maybe just add a comment saying where the other case is handled then!

return false;
}

let numeratorFirstTerm;
if (numerator.op === '+') {
numeratorFirstTerm = new Node.PolynomialTerm(numerator.args[0]);
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I'm concerned that we can just assume it'll be a polynomial term

(what if the second arg is a polynomial term? what if there are more than 2 args?)

Sorry this got more complicated haha. If you want, we can chat on gitter or something and figure out how to attack this

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Yeah, this is what I wanted to talk about actually. One of the main issues is that it's not sorted, so I wanted to ask you all if we should add a sorting function which will run before this. Or if you don't see any merit in that, we could add some logic to find the highest polynomial term right into the function (or outside of it if you want).

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yeah sure, I'm down to chat on gitter

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sweet - okay I actually am busy all day tomorrow >.> (first day of work!!)

does Wed evening work for you?

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or can we chat asynchronously - I can try to think about solutions to this tomorrow

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uhh yeah lets just chat asynchronously then, no worries take your time, good luck!

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@evykassirer evykassirer May 10, 2017 •
edited
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I think you could start with doing this rule only if there are exactly one or two args, the first is always a polynomial term, and the second if it exists is always a constant

i.e. come up with very limited cases and then test for them before going forward and do nothing if none of those cases work

and then after merging this you could add some more cases if they're easy enough

what do you think? @

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oh whoops didn't see this, sure sounds good!

}
else if (numerator.op === '*') {
numeratorFirstTerm = new Node.PolynomialTerm(numerator);
}

let denominatorFirstTerm;
if (denominator.op === '+') {
denominatorFirstTerm = new Node.PolynomialTerm(denominator.args[0]);
}
else if (denominator.op === '*') {
denominatorFirstTerm = new Node.PolynomialTerm(denominator);
}

if (!(numeratorFirstTerm)) {
return false;
}
if (!(denominatorFirstTerm)) {
return false;
}

if (!(numeratorFirstTerm.getSymbolName() === 'x' && denominatorFirstTerm.getSymbolName() === 'x')) {
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I think it's better to just say they have the same symbol. Then if they share the symbol y, it'd work too!

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oh true, I didn't think about the symbol being a different name. The reason I did it to equal 'x' was to restrict it to the case of x^1

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yeah I think just doing getSymbolName() === getSymbolName() would work!

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@eltonlaw eltonlaw May 9, 2017 •
edited
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wait I'm not really getting the use of getSymbolName() actually, what other values can the symbol even take, it seems like it always returns 'x'. I originally thought the getSymbolName would grab the exponent as well, but that's actually covered by getExponentNode.

Is getSymbolName just for when there are multiple variables? Cause that seems way out of the scope for now anyways.

Would it be better to check that denominatorFirstTerm.getExponentNode() === numeratorFirstTerm.getExponentNode() or check if they equal undefined? I guess we could keep the getSymbolName === getSymbolName there just for good measure. Is this correct or am I missing something?

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using getSymbolName makes sure the symbol in numerator and denominator are the same - i.e. both x or both y or whatever - you could take any example with xs and change them to ys and it should also work (actually can you add a test for that? ^_^)

numeratorFirstTerm.getSymbolName() === denominatorFirstTerm.getSymbolName() is what I was thinking

return false;
}

return true;
}

module.exports = canFindDenominatorInNumerator;
2 changes: 2 additions & 0 deletions lib/checks/canSimplifyPolynomialTerms.js
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@@ -1,11 +1,13 @@
const canAddLikeTermPolynomialNodes = require('./canAddLikeTermPolynomialNodes');
const canFindDenominatorInNumerator = require('./canFindDenominatorInNumerator');
const canMultiplyLikeTermPolynomialNodes = require('./canMultiplyLikeTermPolynomialNodes');
const canRearrangeCoefficient = require('./canRearrangeCoefficient');

// Returns true if the node is an operation node with parameters that are
// polynomial terms that can be combined in some way.
function canSimplifyPolynomialTerms(node) {
return (canAddLikeTermPolynomialNodes(node) ||
canFindDenominatorInNumerator(node) ||
canMultiplyLikeTermPolynomialNodes(node) ||
canRearrangeCoefficient(node));
}
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2 changes: 2 additions & 0 deletions lib/checks/index.js
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@@ -1,4 +1,5 @@
const canAddLikeTermPolynomialNodes = require('./canAddLikeTermPolynomialNodes');
const canFindDenominatorInNumerator = require('./canFindDenominatorInNumerator');
const canMultiplyLikeTermPolynomialNodes = require('./canMultiplyLikeTermPolynomialNodes');
const canRearrangeCoefficient = require('./canRearrangeCoefficient');
const canSimplifyPolynomialTerms = require('./canSimplifyPolynomialTerms');
Expand All @@ -8,6 +9,7 @@ const resolvesToConstant = require('./resolvesToConstant');

module.exports = {
canAddLikeTermPolynomialNodes,
canFindDenominatorInNumerator,
canMultiplyLikeTermPolynomialNodes,
canRearrangeCoefficient,
canSimplifyPolynomialTerms,
Expand Down
45 changes: 42 additions & 3 deletions lib/simplifyExpression/breakUpNumeratorSearch/index.js
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@@ -1,3 +1,4 @@
const canFindDenominatorInNumerator = require('../../checks/canFindDenominatorInNumerator');
const ChangeTypes = require('../../ChangeTypes');
const Node = require('../../node');
const TreeSearch = require('../../TreeSearch');
Expand Down Expand Up @@ -27,8 +28,47 @@ function breakUpNumerator(node) {
// At this point, we know that node is a fraction and its numerator is a sum
// of terms that can't be collected or combined, so we should break it up.
const fractionList = [];
const denominator = node.args[1];
numerator.args.forEach(arg => {
let denominator = node.args[1];

// Check if we can add/substract a constant to make the fraction nicer
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substract -> subtract

// fraction e.g. (2+x)/(5+x) -> (5+x)/(5+x) - 3/(5+x)
if (canFindDenominatorInNumerator(node)) {
let denominatorParenRemoved = false;
if (Node.Type.isParenthesis(denominator)) {
denominatorParenRemoved = true;
denominator = denominator.content;
}
const newNumerator = [];

// The constant value difference between the numerator and the denominator
const num_n = numerator.args.length;
const den_n = denominator.args.length;
const numeratorFirstTerm = new Node.PolynomialTerm(numerator.args[0]);
const denominatorFirstTerm = new Node.PolynomialTerm(denominator.args[0]);
const numeratorPolyCoeff = numeratorFirstTerm.getCoeffValue();
const denominatorPolyCoeff = denominatorFirstTerm.getCoeffValue();
const multiplier = numeratorPolyCoeff / denominatorPolyCoeff;

const numeratorConstant = parseInt(numerator.args[num_n-1].value) || 0;
const denominatorConstant = parseInt(denominator.args[den_n-1].value) || 0;
const addedConstant = numeratorConstant - (denominatorConstant * multiplier);

if (multiplier === 1) {
newNumerator.push(denominator);
}
else {
const multiplierNode = Node.Creator.constant(multiplier);
newNumerator.push(Node.Creator.operator('*', [multiplierNode, denominator]));
}
newNumerator.push(Node.Creator.constant(addedConstant));

numerator = newNumerator;

if (denominatorParenRemoved) {
denominator = Node.Creator.parenthesis(denominator);
}
}
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I think it'd be best if we can break this up into two steps. the step you added, and the break up fraction that comes after (and then maybe we can group in the cancelling that comes after). and then we'd have substeps for breaking up the fraction.

what do you think? (let me know if you want me to explain more what this means)

numerator.forEach(arg => {
const newFraction = Node.Creator.operator('/', [arg, denominator]);
newFraction.changeGroup = 1;
fractionList.push(newFraction);
Expand All @@ -41,5 +81,4 @@ function breakUpNumerator(node) {
return Node.Status.nodeChanged(
ChangeTypes.BREAK_UP_FRACTION, node, newNode, false);
}

module.exports = search;
10 changes: 10 additions & 0 deletions test/checks/checks.test.js
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Expand Up @@ -29,3 +29,13 @@ describe('canSimplifyPolynomialTerms addition', function() {
];
tests.forEach(t => testCanCombine(t[0], t[1]));
});

describe('canSimplifyPolynomialTerms denominator in numerator', function() {
const tests = [
['(2x + 3)/(2x + 2)', true],
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can you add a bunch more tests? especially a cases that should be false

you can use some of my comments above for edge cases to test for too :)

['(2x+3)/(2x)', false],
['(5x + 3)/(4)', false],
['(2x)/(2x + 3)', true],
];
tests.forEach(t => testCanCombine(t[0], t[1]));
});
7 changes: 7 additions & 0 deletions test/simplifyExpression/breakUpNumeratorSearch/breakUpNumeratorSearch.test.js
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Expand Up @@ -11,6 +11,13 @@ describe('breakUpNumerator', function() {
['(x+3+y)/3', '(x / 3 + 3/3 + y / 3)'],
['(2+x)/4', '(2/4 + x / 4)'],
['2(x+3)/3', '2 * (x / 3 + 3/3)'],
['(2x + 3)/(2x + 2)', '((2x + 2) / (2x + 2) + 1 / (2x + 2))'],
['(2x - 3)/(2x + 2)', '((2x + 2) / (2x + 2) - 5 / (2x + 2))'],
['(2x + 3)/(2x)', '(2x / (2x) + 3 / (2x))'],
['(3 + 2x)/(2x)', '(3 / (2x) + 2x / (2x))'],
['(4x + 3)/(2x + 2)', '(2 * (2x + 2) / (2x + 2) - 1 / (2x + 2))'],
// ['(2x)/(3 + 2x)', '((3 + 2x) / (3 + 2x) - 3 / (3 + 2x))'],
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why are these commented out?

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As mentioned earlier, I didn't know what to do without some sort of way to sort it.

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ah, cool - sorry for missing that

// ['(2x)/(2x + 3)', '((2x + 3) / (2x + 3)) - 3 / (2x + 3)'],
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if these tests pass, uncomment them

otherwise leave a TODO with what we'll need to do in the future to make them pass

];
tests.forEach(t => testBreakUpNumeratorSearch(t[0], t[1]));
});