# A Step-by-Step Solution Methodology for Mathematical Expressions

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Review of the Literature

#### 2.2. Methodology Illustration

**Phase 1**:- Parser definition
**Steps**: Grammar design, grammar conversion, compiler-compiler input construction, code generation **Phase 2**:- Input data analysis
**Steps**: Token generation, syntax analysis, AST generation **Phase 3**:- Evaluation and interpretation
**Steps**: Solving expressions, simplification, printing intermediate evaluation results.

#### 2.3. Evaluation of Mathematical Expressions

#### 2.3.1. BNF Grammar Definition

Listing 1. An Extended-BNF grammar for mathematical expression. |

G = {Σ, T, V, P, S} V = {expr, op, func, var, number, digit}⊆ Σ T = {x, Sin, Cos, Tan, Log, Exp, Sqrt, +, -, *, /}⊆Σ Σ = T ∪ V, S = { expr } <expr>::= <expr> <op> <expr> |(<expr>) |<func>(<expr>) |<var> |<Number> <op>::=‘+’ | ‘-’ | ‘*’ | ‘/’ | ‘^’ <func>::= ‘Sin’ | ‘Cos’ | ‘Tan’ | ‘Log’ |’Exp’ | ‘Sqrt’ <var>::=‘x’ <number>::= ‘-’ ? <digit> + (‘. ‘ <digit> +)? <digit>::=[‘ 0’-’9’] |

#### 2.3.2. Grammar Conversion

Listing 2. A LL(1) grammar for mathematical expressions. |

G = {Σ, T, V, P, S} V = {expr, element, term, unary, power, func, number, digit}⊆Σ T = {x, Sin, Cos, Tan, Log, Exp, Sqrt, (,), +, -, *, /, ^}⊆Σ Σ = T ∪ V, S = { expr } <expr>→<unary> <term> [(“+” | ”-”) <term>]* <unary>→(“+” | ”-”)? <term>→<power> [(“*” | ”/”)<power>]* <power>→<element> (“^”<power>)? <element>→<func> (<expr>) | <number> | “x” <func>→”Sin “ | “Cos” | “Tan” | “Log” | “Exp” | “Sqrt” <number>→”-”? <digit> + (“.”<digit>+)? <digit>→[“ 0”-”9”] |

#### 2.3.3. Definition of Syntax Classes

Listing 3. The definition of some syntax classes shown in Table 1. |

public abstract class Exp { public Exp exp1, exp2; public Exp (Exp e1, Exp e2){ this.exp1 = e1; this.exp2 = e2; } } public class Plus extends Exp { … } … public class Sin extends Exp { public Sin(Exp e) {super(e, null); } } … public class Num extends Exp { public double num; public Num(double n){ this.num = n; } } public class Var extends Exp { private String var; public Var() { super(null, null) } public Var(String var) { super(null, null); this.var = var; } } |

Listing 4. The definition of some syntax classes for eval() method. |

abstract class Exp { … public abstract double Eval(int x); } class Plus extends Exp { Exp exp1, exp2, tmp; public Plus(Exp e1, Exp e2) { exp1 = e1; exp2 = e2; } public double Eval(int x) { return (exp1.Eval(x)+exp2.Eval(x)); } … } class Minus extends Exp { Exp exp1, exp2; Data val2; Exp tmp; public Minus(Exp e1, Exp e2) { exp1 = e1; exp2 = e2; } public double Eval(int x) { return (exp1.Eval(x)- exp2.Eval(x)); } … } class Times extends Exp { Exp exp1, exp2, tmp; Data val2; public Times(Exp e1, Exp e2) { exp1 = e1; exp2 = e2; } public double Eval(int x) { return (exp1.Eval(x)*exp2.Eval(x)); } … } class Var extends Exp { public Var(String var) { this.var = var; } public double Eval(int x) { return (x); } … } |

#### 2.3.4. Parser Construction

#### Token Specification

Listing 5. JavaCC token declarations of the terminals in the grammar Listing 2. |

TOKEN : { < NUMBER : ([“0”-”9”])+(“.” ([“0”-”9”])+)? > } TOKEN : { < EOL : “\n” > } TOKEN : /* OPERATORS */ { < PLUS: “+” > | < MINUS: “-” > | < TIMES: “*” > | < DIV : “/” > | < POW : “^” > …… } TOKEN : /* FUNCTIONS */ { < SQRT: “sqrt” > | < SIN: “sin” > | < COS: “cos” > …… } TOKEN : /* SYMBOLS */ { < X: “x” > | < LPR: “(“ > | < RPR: “)” > } SKIP : { “ “ | “\t” | “\r” } |

#### Parser Definition

#### 2.3.5. Generating Abstract Syntax Tree (AST)

Listing 6. The Java statements added to produce AST. |

Exp parse() : { Exp a; }{ a = expr() (<EOF> | <EOL>) { return a; } } Exp expr() : { Exp a, b; }{ a = term() ( <PLUS> b = term() { a = new Plus(a, b); } | <MINUS> b = term() { a = new Minus(a, b); } )* { return a; } } … Exp power() : { Exp a, b; }{ a = element() ( <POWER> b = power() { a = new Power(a, b); } )? { return a; } }… Exp element() : { Token t; Exp a; } { t=<NUMBER> { return (new Num(Double.parseDouble(t.image))); } | <X> { return (new Var()); } | <LPR> a = expr() <PPR> { return a;} | <SIN> <LPR> a=expr() <PPR> { return new Sin(a);} … }... |

#### 2.3.6. Evaluation of Mathematical Expressions

#### Direct Evaluation of Mathematical Expressions

^{3}+ 7x + 1” evaluated for x = 2, the combined process of parameter passing and evaluation will return 39.

Listing 7. Some JavaCC functions for string-based evaluation. |

double parse(double x) : { double a; } { a = expr(x) (<EOF> | <EOL>) { return a; } } double expr(double x) : { double a, b; }{ a = term(x) ( <PLUS> b = term(x) { a = a+b; } | <MINUS> b = term(x) { a = a-b; } )* { return a; } } double power(double x) : { double a, b; }{ a = element(x) ( <POWER> b = power(x) { a = Math.pow (a, b); } )? { return a; } } double element(double x) : { Token t; double a;} { t = <NUMBER> { return Double.parseDouble(t.image); } | <X> { return x; } | <LPR> a = expr(x) <RPR> { return a; } | <SIN> <LPR> a = expr(x) <RPR> { return Math.sin(a); } … } |

#### Evaluation of Mathematical Expressions Using AST

#### 2.4. Representation of Mathematical Expressions

#### 2.4.1. Human-Readable Format

#### 2.4.2. LaTex Format

#### 2.4.3. MathML Format

#### 2.5. Automatic Simplification

#### 2.5.1. Similar Operands

Listing 8. Simplifying similar operands for Num and Var in Plus. |

if (exp1 instanceOf Num && exp2 instanceOf Num) return new Num(exp1.getNum()+ exp2.getNum()); if (exp1 instanceOf Var && exp2 instanceOf Var ) return new Times (new Num(2), exp1); |

#### 2.5.2. Similar Operands on Different Levels

Listing 9. Collecting operands for similar operators. |

public ArrayList<Exp> sameOpList (){ ArrayList<Exp> a=new ArrayList<Exp>(); ArrayList<Exp> b=new ArrayList<Exp>(); if(exp1 instanceOf Plus || exp1 instanceOf Minus) a = exp1.sameOpList(); else a.add(exp1); if(exp2 instanceOf Plus || exp2 instanceOf Minus) b = exp2.sameOpList(); else b.add(exp2); return mergeList(a, b); } |

#### 2.5.3. Fraction Simplification

Listing 10. The simplify() method for Divide class. |

public class Divide extends Exp { public Exp simplify() { if (exp1 instanceof Divide || exp2 instanceof Divide){ if (!exp1 instanceof Divide) exp1 = new Divide(exp1, new Num(1)); if (!exp2 instanceof Divide) exp2 = new Divide(exp2, new Num(1)); } … //codes for GCD … return new Divide(exp1.simplify(), exp2.simplify()); } } |

Listing 11. Changes in the simplify() method for Divide class. |

exp1 = new Times(exp1.exp1.simplify(), exp2.exp2.simplify()).simplify(); exp2 = new Times(exp2.exp1.simplify(), exp1.exp2.simplify()).simplify(); … //codes for GCD … |

Listing 12. Modifications in class Plus. |

… if (exp1 instanceOf Divide || exp2 instanceOf Divide){ if (!exp1 instanceOf Divide) exp1 = new Divide (exp1, new Num(1)); if (!exp2 instanceOf Divide) exp2 = new Divide (exp2, new Num(1)); Exp a = exp1.exp1; Exp b = exp1.exp2; Exp c = exp2.exp1; Exp d = exp2.exp2; Exp G = polynomialLCM (b, d); a = new Times (a, polynomialDivide(G, b).result); c = new Times (c, polynomialDivide(G, d).result); return new Divide(new Plus(a, c), G); } … |

#### 2.5.4. Exponential Simplifications

^{a*b*c}in terms of left-associativity.

Listing 13. Simplify method for Power class. |

public class Power extends Exp { … public ArrayList<Exp> sameOpList(){ ArrayList<Exp> a = new ArrayList<Exp>(); if(exp2 instanceOf Power ) return mergeList(a, exp2.sameOpList()); else return exp2.simplify(); } … public Exp simplify() { Exp b = exp1.exp1; Exp e = new Num(1); ArrayList<Exp> pow = sameOpList(); for(Exp tmp: pow) e = new Times(e, tmp); return new Power(b, e); } … } |

^{n}.v

^{n}and u

^{n}.v

^{m}.

#### 2.5.5. Removal of Radical Expression in Denomination

Listing 14. Simplify method for Divide class. |

… if (exp2 instanceof Sqrt){ Exp sq = exp2.exp1; return new Divide(new Times(exp1, sq), sq); } … |

#### 2.5.6. Equality of Expressions

Listing 15. Equality of mathematical expressions. |

public class Exp{ public boolean isEqual(Exp e) { Exp a = this.simplify(); Exp b = e.simplify(); if(a.eval().equal(“0”) && b.eval().equal(“0”)) return true; Exp res = new Divide(a, b); return res.eval().equal(“0”); } } |

#### 2.5.7. Other Simplifications

- ${x}^{2}+\left(a+b\right)x+a.b\text{}=\left(x+a\right).\left(x+b\right)$
- ${x}^{2a}-{y}^{2b}=\left({x}^{a}+{y}^{b}\right).\left({x}^{a}-{y}^{b}\right)$
- $\mathrm{Sin}\text{}\left(\text{}exp1+\text{}exp2\right)=\mathrm{Sin}\left(exp1\right)\ast \mathrm{Cos}\left(exp2\right)+\text{}\mathrm{Cos}\left(exp1\right)\ast \mathrm{Sin}\left(exp2\right)$
- ${a}^{2}-2ab+{b}^{2}={\left(a-\mathrm{b}\right)}^{2}$
- ${a}^{3}+{b}^{3}=\left(a+b\right).\left({a}^{2}-ab+{b}^{2}\right)$
- ${a}^{3}-{b}^{3}=\left(a-b\right).\left({a}^{2}+ab+{b}^{2}\right)$

#### 2.6. Controlling the Step-by-Step Solution

- Print the transformation into an output buffer, and continue.
- Return to the root node after performing each transformation

Listing 16. The main loop for simplifications. |

public Exp performSimplification(Exp root){ do{ Controls.resetFlags(); root = root.simplify(); if(Controls.hasError() != null){ System.out.println(Controls.getError()); return null; } root.Print(); } while ( Controls.isSkipSimplifying() ); root.Print(); return root; } |

Listing 17. Modifications for the simplify() method. |

public Exp simplify(){ if(Controls.isSkipSimplifying()) return this; … // rest of the codes simplifying the element … // in case of performing any // simplification call Controller.skipSimplification(); … } |

#### Expression Simplification Control

Listing 18. The control of the simplification of radical removal using control flags. |

public Exp simplify(){ if(Controls.isSkipSimplifying()) return this; … if (exp2 instanceof Sqrt && Controls.isSqrtRemoveal()){ Exp sq = exp2.exp1; // Notify the transformation to controller Controller.skipSimplification(); return new Divide(new Times(exp1, sq), sq); } … } |

## 3. Conclusions and Results

## Author Contributions

## Funding

## Conflicts of Interest

## References

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Component | Syntax Format | Syntax Class | Attributes |
---|---|---|---|

+ | Exp + Exp | Plus | exp1, exp2 |

* | Exp * Exp | Times | exp1, exp2 |

^ | Exp ^ Exp | Power | exp1, exp2 |

Sin | Sin(Exp) | Sin | exp |

Cos | Cos(Exp) | Cos | exp |

Numbers | n | Num | n |

Variables | ---- | Var | ---- |

Normal Rules | Combined Rules |
---|---|

< expr >→< term > < expr’ > < expr’ >→(“+” | ”-”) < term > < expr’ > < expr’ >→λ | < expr >→< term > { (“+” | ”-”) < term > }* |

< term >→< unary > < term’ > < term’ >→(“*” | ”/”) < unary > < term’ > < term’ >→λ | < term >→ < unary >{ (“*” | ”/”) < unary >}* |

Grammar Rule | Corresponding Method |
---|---|

< start >→< expr > $ | void parse() : { } { expr() (<EOF> | <EOL>) } |

< expr >→< term > { (“+” | ”-”) < term > }* | void expr() : { }{ term()( <PLUS> term() | <MINUS> term() )* } |

< power >→< element > (“^”< power >)? | void power() : { }{ element() ( <POWER> power() )? } |

Class Name | Print Method |
---|---|

Exp | public String Print() { return ““; } public static String Out(String str) { if( str.contains(“-”) || str.contains(“+”) || str.contains(“*”) || str.contains(“/”) ) str = “(“ + str + “)”; return str; } |

Plus | public String Print() { String a = exp1.print(); String b = exp2.print(); return Exp.Out(a) + “+” + Exp.Out(b); } |

Minus | public String Print() { String a = exp1.print(); String b = exp2.print(); return Exp.Out(a) +”-” + Exp.Out(b); } |

Times | public String Print() { String a = exp1.print(); String b = exp2.print(); return Exp.Out(a) + “*” + Exp.Out(b); } |

Functions | public String Print() { return “sin(“ + exp.Print() + “)”; } |

Num | public String Print() { return Integer.toString(num); } |

Class Name | LaTex Method |
---|---|

Exp | public String LaTex() { return ““; } public static String Out(String str) { if( str.contains(“-”) || str.contains(“+”) || str.contains(“*”) || str.contains(“/”)) str = “(“ + str + “)”; return str; } |

Plus | public String LaTex() { String a = exp1.LaTex(); String b = exp2.LaTex(); return Exp.Out(a) + “+” + Exp.Out(b); } |

Divide | public String Print() { String a = exp1.LaTex(); String b = exp2.LaTex(); return “\\frac {“ + a + “} {“ + b + “}”; } |

Power | public String LaTex() { String a = exp1.LaTex(); String b = exp2.LaTex(); return “(“ + a + “) ^ {“ + b + “}”; } |

Functions | public String LaTex() { return “\\sin {“ + exp.Print() + “}”; } |

Num | public String LaTex() { return Integer.toString(num); } |

Class Name | MathML Method |
---|---|

Exp | public String MathML() { return ""; } |

Plus | public String MathML() { String a = exp1.MathML(); String b = exp2.MathML(); return "<mi>" + a + "<mo>+</mo>" + b + "</mi>"; } |

Divide | public String MathML() { String a = exp1.MathML(); String b = exp2.MathML(); return "<mfrac>" + a + b + "</mfrac>"; } |

Times | public String MathML() { String a = exp1.MathML(); String b = exp2.MathML(); "<mi>" + a + "*" + b + "</mi>"; } |

Functions | public String MathML() { return "<mi>sin</mi>" + "<mi>" + exp.MathML() + "<mi>"; } |

Num | public String MathML() { return "<mn>" + Integer.toString(num) + "<mn>"; } |

Raw View | Rendered View |
---|---|

<math xmlns="http://www.w3.org/1998/Math/MathML"> <mfrac> <mrow> <mo>(</mo> <mn>3</mn> <mi>sin</mi> <mo>(</mo> <mi>x</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> <mo>)</mo> </mrow> <mn>2</mn> </mfrac> </math> | $\frac{\left(3\mathrm{sin}\left(x+1\right)\right)}{2}$ |

Original Term | Object Tree | Simplification Results |
---|---|---|

0 + exp | Plus (Num (0), exp) | exp |

exp + 0 | Plus (exp, Num (0)) | exp |

0 − exp | Minus (Num (0), exp) | Times (Num (−1), exp) |

exp − 0 | Minus (exp, Num (0)) | exp |

0 * exp | Times (Num (0), exp) | Num (0) |

exp * 0 | Times (exp, Num (0)) | Num (0) |

1 * exp | Times (Num (1), exp)) | exp |

exp * 1 | Times (exp, Num (1)) | exp |

0/exp | Divide (Num (0), exp)) | Num (0) |

exp/1 | Divide (exp, Num (1)) | exp |

Class Name | Corresponding Method |
---|---|

Exp | public abstract Exp Simplify(); |

Plus | public Exp Simplify() { Exp e1 = exp1.Simplify(); Exp e2 = exp2.Simplify(); if (e1.eval().equals(“0”)) return e2; if (e2.eval().equals(“0”)) return e1; return new Plus(e1, e2); } |

Times | public Exp Simplify() { Exp e1 = exp1.Simplify(); Exp e2 = exp1.Simplify(); if (e1.eval().equals(“0”)) return new Num(0); if (e2.eval().equals(“0”)) return new Num(0); if (e1.eval().equals(“1”)) return e2; if (e2.eval().equals(“1”)) return e1; return new Times(e1, e2); } |

Sin | Public Exp Simplify() { return new Sin(exp.Simplify); } |

Variable Name | Usage |
---|---|

isSkipSimplifying | Status of simplification |

isExapnding | Expand algebraic formulas |

isSqrtRemoveal | Remove radicals in denomination |

isPowerSimplify | Exponential simplification |

isMergeFractions | Merge fractions |

……… |

Expression | Matlab | A Real Person | Our System |
---|---|---|---|

x + 3x + 2 | 4x + 2 | 4x + 2 | 4x + 2 |

2x(x^{2} + 2x + 1) | 2x(x + 1)^{2} | 2x^{3} + 4x^{2} + 2x | 2x^{3} + 4x^{2} + 2x |

(2x − 1)(3x + 1) | (2x − 1)(3x + 1) | 6x^{2} − x − 1 | 6x^{2} − x − 1 |

${({({2}^{a})}^{b})}^{3}$ | ${({2}^{a})}^{3b}$ | 2^{3ab} | 2^{3ab} |

${2}^{({a}^{({b}^{3})})}$ | ${2}^{({a}^{({b}^{3})})}$ | ${2}^{({a}^{({b}^{3})})}$ | ${2}^{({a}^{({b}^{3})})}$ |

$\frac{{x}^{2}-2x+1}{x-1}$ | x − 1 | x − 1 | x − 1 |

Expression | Number of Terms | Step-by-Step Solution | Fast Solution | ||
---|---|---|---|---|---|

Recalls | Average | Recalls | Average | ||

x + 3x + 2 | 3 | 5 | 1.67 | 3 | 1 |

2x(x^{2} + 2x + 1) | 4 | 18 | 4.5 | 13 | 3.25 |

(2x − 1)(3x + 1) | 4 | 16 | 4 | 11 | 2.75 |

${({({2}^{a})}^{b})}^{3}$ | 3 | 5 | 1.67 | 3 | 1 |

${2}^{({a}^{({b}^{3})})}$ | 3 | 3 | 1 | 3 | 1 |

$\frac{{x}^{2}+2x-1}{x-1}$ | 5 | 9 | 1.8 | 4 | 0.8 |

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Hosseinpour, S.; Alavi Milani, M.M.R.; Pehlivan, H.
A Step-by-Step Solution Methodology for Mathematical Expressions. *Symmetry* **2018**, *10*, 285.
https://doi.org/10.3390/sym10070285

**AMA Style**

Hosseinpour S, Alavi Milani MMR, Pehlivan H.
A Step-by-Step Solution Methodology for Mathematical Expressions. *Symmetry*. 2018; 10(7):285.
https://doi.org/10.3390/sym10070285

**Chicago/Turabian Style**

Hosseinpour, Sahereh, Mir Mohammad Reza Alavi Milani, and Hüseyin Pehlivan.
2018. "A Step-by-Step Solution Methodology for Mathematical Expressions" *Symmetry* 10, no. 7: 285.
https://doi.org/10.3390/sym10070285