/*
* Redberry: symbolic tensor computations.
*
* Copyright (c) 2010-2013:
* 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.transformations;
import cc.redberry.core.tensor.Product;
import cc.redberry.core.tensor.ScalarsBackedProductBuilder;
import cc.redberry.core.tensor.Tensor;
import cc.redberry.core.tensor.iterator.FromChildToParentIterator;
import cc.redberry.core.tensor.iterator.TraverseGuide;
import cc.redberry.core.utils.TensorUtils;
/**
* Puts together similar scalar subproducts in each product. For example, tensor A_m*A^m*A_n*A^n
* will be transformed to tensor (A_m*A^m)**2.
*
* @author Dmitry Bolotin
* @author Stanislav Poslavsky
* @since 1.1
*/
public class CollectScalarFactorsTransformation implements Transformation {
/**
* Singleton default instance.
*/
public static final CollectScalarFactorsTransformation COLLECT_SCALAR_FACTORS
= new CollectScalarFactorsTransformation();
private final TraverseGuide traverseGuide;
private CollectScalarFactorsTransformation() {
this.traverseGuide = TraverseGuide.ALL;
}
/**
* Creates transformation for particular parts of expressions, specified by traverse guide.
*
* @param traverseGuide specifies parts of expression to apply the transformation
*/
public CollectScalarFactorsTransformation(TraverseGuide traverseGuide) {
this.traverseGuide = traverseGuide;
}
@Override
public Tensor transform(Tensor t) {
return collectScalarFactors(t, traverseGuide);
}
/**
* Puts together similar scalar subproducts in each product. For example, tensor A_m*A^m*A_n*A^n
* will be transformed to tensor (A_m*A^m)**2.
*
* @param tensor tensor
* @return the result
*/
public static Tensor collectScalarFactors(Tensor tensor) {
return collectScalarFactors(tensor, TraverseGuide.ALL);
}
/**
* Puts together similar scalar subproducts in each product of expression, which can
* be traversed with specified traverse guide.
*
* @param tensor tensor
* @param traverseGuide specifies parts of expression to apply the transformation
* @return the result
*/
public static Tensor collectScalarFactors(Tensor tensor, TraverseGuide traverseGuide) {
FromChildToParentIterator iterator = new FromChildToParentIterator(tensor, traverseGuide);
Tensor current;
while ((current = iterator.next()) != null) {
if (current instanceof Product)
iterator.set(collectScalarFactorsInProduct((Product) current));
}
return iterator.result();
}
/**
* Puts together similar scalar subproducts in a given product. For example, tensor A_m*A^m*A_n*A^n
* will be transformed to tensor (A_m*A^m)**2.
*
* @param product product
* @return the result
*/
public static Tensor collectScalarFactorsInProduct(Product product) {
if (TensorUtils.isSymbolic(product))
return product;
ScalarsBackedProductBuilder builder = new ScalarsBackedProductBuilder(product.size(), 1, product.getIndices().getFree().size());
builder.put(product);
return builder.build();
}
}