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Symbols.java
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155 lines (142 loc) · 4.2 KB
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package symjava.symbolic;
import java.util.HashMap;
import java.util.List;
import symjava.symbolic.utils.Utils;
/**
* An object of Symbols can represents a list of symbols
* For example:
* Symbols ss = new Symbols("x"); //x_i, i=...,1,2,3...
* Symbol x1 = ss.get(1); //x_1
* Symbol x8 = ss.get(8); //x_8
*
* This can be used to generate a list of symbols in summation
* or as a parameter list in an equation.
*
* @author yuemingliu
*
*/
public class Symbols extends Expr {
Expr namePrefix;
Expr indexExpr;
HashMap<Integer, Symbol> cache = new HashMap<Integer, Symbol>();
/**
* Create symbols like:
* x_i, i=...,1,2,3,...
* @param namePrefix
*/
public Symbols(String namePrefix) {
this.namePrefix = new Symbol(namePrefix);
this.indexExpr = new Symbol("i");
this.label = namePrefix + "_" +indexExpr;
sortKey = label;
}
/**
* Create more complicated symbols like
* x_{i+j}, i=...,1,2,3,...
* x_{i-1}, i=...,1,2,3,...
*
* @param namePrefix
* @param indexExpr
*/
public Symbols(String namePrefix, Expr indexExpr) {
this.namePrefix = new Symbol(namePrefix);
this.indexExpr = indexExpr;
if(indexExpr instanceof Symbol)
this.label = namePrefix + "_" + indexExpr;
else
this.label = namePrefix + "_{" + indexExpr+"}";
sortKey = label;
}
public Symbol get(int index) {
Symbol s = cache.get(index);
if(s == null) {
if(indexExpr instanceof Symbols) {
s = new Symbol(namePrefix+"_"+index);
cache.put(index, s);
} else {
List<Expr> exprs = Utils.extractSymbols(indexExpr);
if(exprs.size() > 1) {
throw new RuntimeException("Please call get(Expr indexSymbol, int index).");
} else if(exprs.size() == 1){
Expr indexSymbol = exprs.get(0);
Expr simpliedIndexExpr = indexExpr.subs(indexSymbol, index).simplify();
if(simpliedIndexExpr instanceof Symbol || simpliedIndexExpr instanceof SymReal)
s = new Symbol(namePrefix+"_"+simpliedIndexExpr.getLabel());
else
s = new Symbol(namePrefix+"_{"+simpliedIndexExpr.getLabel()+"}");
cache.put(index, s);
} else {
throw new RuntimeException("No indexes found!");
}
}
}
return s;
}
public Symbol get(Symbol indexSymbol, int index) {
Symbol s = cache.get(index);
if(s == null) {
Expr simpliedIndexExpr = indexExpr.subs(indexSymbol, index).simplify();
if(simpliedIndexExpr instanceof Symbol || simpliedIndexExpr instanceof SymReal)
s = new Symbol(namePrefix.getLabel() + "_"+simpliedIndexExpr.getLabel());
else
s = new Symbol(namePrefix.getLabel() + "_{"+simpliedIndexExpr.getLabel()+"}");
cache.put(index, s);
}
return s;
}
/**
* Return an array of symbols: [startIdx, endIdx]
* which include startIdx and endIdx
* @param startIdx
* @param endIdx
* @return
*/
public Expr[] get(int startIdx, int endIdx) {
Expr[] rlt = new Expr[endIdx-startIdx+1];
for(int i=startIdx; i<=endIdx; i++)
rlt[i-startIdx] = get(i);
return rlt;
}
/**
* The substitution of symbols will return a symbol
* which behaves different from other class in SymJava
*/
@Override
public Expr subs(Expr from, Expr to) {
if(Utils.symCompare(this, from)) {
return to;
} else if(Utils.symCompare(indexExpr,from)) {
if(to instanceof SymInteger) {
SymInteger index = (SymInteger)to;
Symbol s = this.get(index.getValue());
//case: symbols.subs(i,3): x_i => x_3
return s;
}
//case: symbols.subs(i,j): x_i => x_j
return new Symbol(namePrefix.getLabel() + "_{" + to + "}");
}
Expr simpliedIndexExpr = indexExpr.subs(from, to).simplify();
if(simpliedIndexExpr instanceof Symbol || simpliedIndexExpr instanceof SymReal)
return new Symbol(this.namePrefix.getLabel() + "_" + simpliedIndexExpr.getLabel());
else
return new Symbol(this.namePrefix.getLabel() + "_{" + simpliedIndexExpr.getLabel() + "}");
}
@Override
public Expr diff(Expr expr) {
if(Utils.symCompare(this, expr))
return Symbol.C1;
return Symbol.C0;
}
@Override
public Expr simplify() {
return this;
}
@Override
public boolean symEquals(Expr other) {
if(other instanceof Symbols) {
return this.namePrefix.equals(((Symbols) other).namePrefix) &&
Utils.symCompare(this.indexExpr, ((Symbols) other).indexExpr);
}
return false;
}
}