CostFunctor

package org.somelightprojections.skeres

import scala.reflect.ClassTag
import spire.algebra.{Trig, Field}

// Generic autodifferentiable cost functor:
//   kNumResiduals: output dimension.
//   N: sequence of integers, ordinately equal to the 
//      dimensions of the parameters blocks.  
abstract class CostFunctor(val kNumResiduals: Int, val N: Int*) {
  require(kNumResiduals > 0, s"Nonpositive number of residuals specified: $kNumResiduals")
  require(N.forall(_ > 0), s"Nonpositive parameter block sizes specified: ${N.mkString(", ")}")

  // Returns an auto-differentiable cost function computed through this functor.
  def toAutodiffCostFunction = AutodiffCostFunction(this)

  // Evaluate the functor on a sequence of N.length parameter blocks, ordinately of N(k) size,
  // for k = 0, 1, ..., N.length.
  def apply[@specialized(Double) T : Field : Trig : ClassTag](x: Array[T]*): Array[T]
}