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1 package JSci.maths.symbolic;
2
3 import JSci.maths.*;
4 import JSci.maths.groups.*;
5 import JSci.maths.fields.*;
6
7 import java.util.*;
8
9 class Product extends Expression {
10
11 private final List terms;
12
13 public Product(Expression [] a) {
14 terms = Arrays.asList(a);
15 }
16
17 public Product(List a) {
18 terms = a;
19 }
20
21 public Product(Expression a,Expression b) {
22 terms = new ArrayList();
23 terms.add(a);
24 terms.add(b);
25 }
26
27 public String  toString() {
28 String r = "";
29 Expression f;
30 for (int j=0;j<terms.size();j++) {
31 if (j>0) r+="*";
32 f=(Expression)terms.get(j);
33 if (f.getPriority()<getPriority()) r+="("+f+")";
34 else r+=""+f;
35 }
36 return r;
37 }
38
39 public Expression differentiate(Variable x) {
40 List r = new ArrayList();
41 List p;
42 for (int j=0;j<terms.size();j++) {
43 p = new ArrayList();
44 for (int k=0;k<terms.size();k++) {
45 if (j==k) p.add(((Expression)terms.get(k)).differentiate(x));
46 else p.add(((Expression)terms.get(k)));
47 }
48 r.add(new Product(p));
49 }
50 return new Sum(r);
51 }
52
53 public Expression evaluate() {
54 List t = new ArrayList();
56 for (int j=0;j<terms.size();j++) {
57 Expression f=((Expression)terms.get(j)).evaluate(); if (Product.class.isInstance(f))
59 for (int k=0;k<((Product)f).terms.size();k++)
60 t.add(((Product)f).terms.get(k));
61 else t.add(f);
62 }
63 Ring.Member c = null;
65 List s = new ArrayList();
66 for (int j=0;j<t.size();j++) {
67 Expression f=(Expression)t.get(j);
68 if (f instanceof Constant) {
69 if (c==null) c=(Ring.Member)(((Constant)f).getValue());
70 else c = c.multiply((Ring.Member)((Constant)f).getValue());
71 }
72 else s.add(f);
73 }
74 if (c!=null && ((AbelianGroup)(c.getSet())).isZero(c))
75 return new Constant(c);
76 if (c!=null && ! (((Ring)(c.getSet())).isOne(c)))
77 s.add(new Constant(c));
78 Hashtable h = new Hashtable();
80 for (int j=0;j<s.size();j++) {
81 Expression b;
82 int e;
83 if (s.get(j) instanceof Power) {
84 b = ((Power)s.get(j)).getBase();
85 e = ((Power)s.get(j)).getExponent();
86 }
87 else {
88 b = (Expression) s.get(j);
89 e = 1;
90 }
91 if (h.containsKey(b))
92 e+=((Integer )h.get(b)).intValue();
93 h.put(b,new Integer (e));
94 }
95 s = new ArrayList();
97 for (Enumeration fe=h.keys();fe.hasMoreElements();) {
98 Expression b = (Expression)fe.nextElement();
99 int e = ((Integer )h.get(b)).intValue();
100 if (e!=0) {
101 if (e==1) s.add(b);
102 else if (e!=0) s.add(new Power(b,e));
103 }
104 }
105 if (s.size()==0) return new Constant(((Ring)getSet()).one());
107 if (s.size()==1) return (Expression)s.get(0);
108 return new Product(s);
109 }
110
111 protected int getPriority() {return 10;}
112
113 public Object getSet() { return ((Member)terms.get(0)).getSet(); }
114
115 }
116
117
118 |
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