/// <summary>
/// Get a partial derivative.
/// </summary>
/// <param name="orders">derivation orders with respect to each variable (if all
/// orders are 0, the value is returned)</param>
/// <returns>partial derivative</returns>
/// <exception cref="DimensionMismatchException">if the numbers of variables does not
/// match the instance</exception>
/// <exception cref="NumberIsTooLargeException"> if sum of derivation orders is larger
/// than the instance limits</exception>
/// <remarks>
/// See <see cref="getValue()"/>
/// </remarks>
public double getPartialDerivative(params int[] orders)
{
return(data[compiler.getPartialDerivativeIndex(orders)]);
}