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package symjava.math;

import java.util.HashSet;

import symjava.matrix.ExprMatrix;

import symjava.relational.Eq;

import symjava.symbolic.Expr;

import symjava.symbolic.Func;

import symjava.symbolic.Symbol;

import symjava.symbolic.utils.Utils;

/**

* Transformation is a system of equations that define the change of variables

* For example:

* x = r + s

* y = r - s

* This will change (x,y) to (r+s, r-s)

*

*/

public class Transformation {

public Eq[] eqs = null;

public Transformation(Eq ...eqs) {

for(Eq e : eqs) {

if(!(e.arg1 instanceof Symbol || e.arg1 instanceof Func))

throw new RuntimeException("The left hand side must be a symbol or function!");

}

this.eqs = eqs;

}

public Expr[] getFromVars() {

Expr[] rlt = new Expr[eqs.length];

for(int i=0; i<rlt.length; i++) {

rlt[i] = eqs[i].arg1;

}

return rlt;

}

public Expr[] getToVars() {

Expr[] rlt = new Expr[eqs.length];

HashSet<Expr> set = new HashSet<Expr>();

for(Eq e : eqs) {

Expr[] freeVars = e.getFreeVars();

for(Expr expr : freeVars)

set.add(expr);

}

rlt = set.toArray(new Expr[0]);

Utils.sortExprs(rlt);

return rlt;

}

public Expr getJacobian() {

return getJacobianMatrix().det();

}

public ExprMatrix getJacobianMatrix() {

Expr[] fromVars = this.getFromVars();

Expr[] toVars = this.getToVars();

ExprMatrix m = new ExprMatrix(fromVars.length, toVars.length);

for(int i=0; i<fromVars.length; i++) {

for(int j=0; j<toVars.length; j++) {

m.set(i, j, eqs[i].arg2.diff(toVars[j]));

}

}

return m;

}

}