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/* |
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$Id$ |
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Copyright (C) 2006 Jari Häkkinen, Nicklas Nordborg |
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This file is part of BASE - BioArray Software Environment. |
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Available at http://base.thep.lu.se/ |
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|
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BASE is free software; you can redistribute it and/or |
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modify it under the terms of the GNU General Public License |
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as published by the Free Software Foundation; either version 3 |
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of the License, or (at your option) any later version. |
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|
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BASE is distributed in the hope that it will be useful, |
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but WITHOUT ANY WARRANTY; without even the implied warranty of |
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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GNU General Public License for more details. |
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|
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You should have received a copy of the GNU General Public License |
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along with BASE. If not, see <http://www.gnu.org/licenses/>. |
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*/ |
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package net.sf.basedb.util.jep; |
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|
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import net.sf.basedb.core.BaseException; |
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import net.sf.basedb.core.query.Expression; |
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import net.sf.basedb.core.query.Expressions; |
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|
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import java.util.Stack; |
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|
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import org.nfunk.jep.Node; |
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import org.nfunk.jep.ParseException; |
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|
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|
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/** |
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A JEP function class that adds a <code>log2(expression)</code> function to a |
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JEP expression parser. The function will look take the 2-based logarithm of |
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it's argument. |
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<p> |
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This function is added automatically by the {@link Jep#newJep(String, JepFunction[])} |
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method to the parser. |
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|
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@author Nicklas |
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@version 2.0 |
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@base.modified $Date$ |
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@see Jep |
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*/ |
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public class Log2Function |
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implements JepExpressionFunction |
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{ |
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|
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/** |
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Get the singleton instance of this function. |
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@return The Log2Function object |
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*/ |
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public static Log2Function getInstance() |
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{ |
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return theInstance; |
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} |
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|
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/** |
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The one and only instance of this function. |
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*/ |
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private static final Log2Function theInstance = new Log2Function(); |
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|
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/** |
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The natural logarithm of 2. This is used when calculating the 2-based |
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logarithm of a value since it can be calculated as: <code>ln(x) / ln(2)</code> |
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*/ |
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private static final double LOG2 = Math.log(2); |
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|
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/** |
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Create a new instance of this function. |
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*/ |
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private Log2Function() |
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{} |
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|
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/* |
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From the JepFunction interface |
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------------------------------------------- |
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*/ |
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/** |
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@return The string "log2" |
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*/ |
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@Override |
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public String getFunctionName() |
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{ |
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return "log2"; |
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} |
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// ------------------------------------------- |
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/* |
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From the JepExpressionFunction interface |
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------------------------------------------- |
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*/ |
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/** |
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Use the {@link Expressions#log2(Expression)} method to create an |
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expression taking the 2-based logarithm of the argument. |
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*/ |
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@Override |
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public Expression toExpression(Node node) |
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{ |
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int numChildren = node.jjtGetNumChildren(); |
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if (numChildren != 1) |
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{ |
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throw new BaseException("Invalid number of arguments for 'log2' function: " + numChildren); |
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} |
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return Expressions.log2(Jep.nodeToExpression(node.jjtGetChild(0))); |
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} |
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// ------------------------------------------- |
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/* |
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From the PostfixMathCommandI interface |
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------------------------------------------- |
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*/ |
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/** |
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@return Always 1 |
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*/ |
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@Override |
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public int getNumberOfParameters() |
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{ |
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return 1; |
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} |
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@Override |
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public void setCurNumberOfParameters(int n) |
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{} |
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@Override |
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public boolean checkNumberOfParameters(int n) |
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{ |
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return n == 1; |
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} |
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@Override |
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@SuppressWarnings({"unchecked", "rawtypes"}) |
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public void run(Stack stack) |
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throws ParseException |
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{ |
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if (stack == null || stack.empty()) |
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{ |
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throw new ParseException("Stack is empty"); |
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} |
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Object argument = stack.pop(); |
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if (argument instanceof Number) |
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{ |
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stack.push(log2((Number)argument)); |
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} |
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else |
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{ |
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throw new ParseException("Invalid parameter type: " + argument + "; expected number"); |
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} |
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} |
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// ------------------------------------------- |
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|
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/** |
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Calculate the 2-based logarithm of the argument. |
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@param argument A number to calculate on |
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@return a double object |
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@throws ParseException If the logarithm could not be calculated. |
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*/ |
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public double log2(Number argument) |
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throws ParseException |
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{ |
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return Math.log(argument.doubleValue()) / LOG2; |
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} |
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} |