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Tensorics is a java framework which uses a tensor as a central object. A tensor represents a set of values placed in an N-dimensional space. Wherever you are tempted to use maps of maps, a tensor might be a good choice ;-) Tensorics provides methods to create, transform and performing calculations with those tensors.

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// @formatter:off
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 *
 * This file is part of tensorics.
 * 
 * Copyright (c) 2008-2011, CERN. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
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// @formatter:on

package org.tensorics.incubate.function;

import static javax.measure.unit.Unit.ONE;

import javax.measure.quantity.Dimensionless;
import javax.measure.quantity.Quantity;

import org.jscience.physics.amount.Amount;
import org.tensorics.core.tensor.Tensor;

import com.google.common.base.Preconditions;

/**
 * @author agorzaws
 * @param  type of arguments
 * @param  type of values
 */
public class ExponentialFunction implements
        AnalyticalFunction, Amount> {

    private final Amount inverseExpConst;
    private final Amount amplitude;

    ExponentialFunction(Builder builder) {
        this.amplitude = builder.amplitude;
        this.inverseExpConst = builder.inverseExpConst;

        Preconditions.checkArgument(amplitude != null, "Argument '" + "amplitude" + "' must not be null!");
        Preconditions.checkArgument(inverseExpConst != null, "Argument '" + "inverseExponentialConstant"
                + "' must not be null!");
    }

    @Override
    public Amount getY(Amount xValue) {
        /* cast is safe since x and inverseExpConst are the same Dimension */
        @SuppressWarnings("unchecked")
        Amount divisionResult = (Amount) xValue.divide(inverseExpConst);
        return amplitude.times(Math.exp(divisionResult.doubleValue(ONE)));
    }

    @Override
    public String toText() {
        return "[y = A * exp(x / B)]";
    }

    public Amount getAmplitude() {
        return amplitude;
    }

    public Amount getInverseExponentialConstant() {
        return inverseExpConst;
    }

    /**
     * An builder for an exponentional functions that uses jscience amounts.
     * 
     * @author agorzaws
     * @param  the type of quantity in X direction
     * @param  the type of quantity in Y direction
     */
    public static final class Builder {

        private Amount inverseExpConst;
        private Amount amplitude;

        Builder() {
            /* package private constructor to allow instantion only from the factory method */
        }

        public Builder withAmplitude(Amount newAmplitude) {
            this.amplitude = newAmplitude;
            return this;
        }

        public Builder withInverseExponentialConstant(Amount newInverseExpConst) {
            this.inverseExpConst = newInverseExpConst;
            return this;
        }

        public ExponentialFunction build() {
            return new ExponentialFunction<>(this);
        }
    }

    public static  Builder builder() {
        return new Builder<>();
    }

    public Tensor> tensor() {
        throw new UnsupportedOperationException("Cannot get a discrete tensor from analytical function");
    }
}