/*
* Redberry: symbolic tensor computations.
*
* Copyright (c) 2010-2014:
* Stanislav Poslavsky <stvlpos@mail.ru>
* Bolotin Dmitriy <bolotin.dmitriy@gmail.com>
*
* This file is part of Redberry.
*
* Redberry is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Redberry is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Redberry. If not, see <http://www.gnu.org/licenses/>.
*/
package cc.redberry.core.tensor;
import cc.redberry.core.context.OutputFormat;
import cc.redberry.core.indices.Indices;
import cc.redberry.core.transformations.Transformation;
import cc.redberry.core.transformations.substitutions.SubstitutionTransformation;
import cc.redberry.core.utils.TensorUtils;
/**
* Representation of mathematical expression <i>A = B</i>. {@code Expression} also implements
* {@link Transformation} and represents substitutions.
*
* @author Dmitry Bolotin
* @author Stanislav Poslavsky
* @see ExpressionBuilder
* @see ExpressionFactory
* @since 1.0
*/
public class Expression extends Tensor implements Transformation {
private final Tensor right, left;
private final Indices indices;
Expression(Indices indices, Tensor left, Tensor right) {
this.indices = indices;
this.right = right;
this.left = left;
}
@Override
public Tensor get(int i) {
switch (i) {
case 0:
return left;
case 1:
return right;
default:
throw new IndexOutOfBoundsException();
}
}
@Override
public Indices getIndices() {
return indices;
}
@Override
protected int hash() {
return 3 * left.hashCode() - 7 * right.hashCode();
}
@Override
public int size() {
return 2;
}
@Override
public String toString(OutputFormat mode) {
return left.toString(mode) + " = " + right.toString(mode);
}
@Override
public TensorBuilder getBuilder() {
return new ExpressionBuilder();
}
@Override
public TensorFactory getFactory() {
return ExpressionFactory.FACTORY;
}
@Override
public Tensor transform(Tensor t) {
return new SubstitutionTransformation(this).transform(t);
}
/**
* Returns {@code true} if r.h.s. is equal to l.h.s.
*
* @return {@code true} if r.h.s. is equal to l.h.s.
*/
public boolean isIdentity() {
return TensorUtils.equals(left, right);
}
/**
* Swaps l.h.s. and r.h.s. of expression.
*
* @return swapped expression
*/
public Expression transpose() {
return new Expression(indices, right, left);
}
}