util.go

package goop

import (
	log "github.com/sirupsen/logrus"
)

// Sum returns the sum of the given expressions. It creates a new empty
// expression and adds to it the given expressions.
func Sum(exprs ...Expr) Expr {
	newExpr := NewExpr(0)
	for _, e := range exprs {
		newExpr.Plus(e)
	}

	return newExpr
}

// SumVars returns the sum of the given variables. It creates a new empty
// expression and adds to it the given variables.
func SumVars(vs ...*Var) Expr {
	newExpr := NewExpr(0)
	for _, v := range vs {
		newExpr.Plus(v)
	}
	return newExpr
}

// SumRow returns the sum of all the variables in a single specified row of
// a variable matrix.
func SumRow(vs [][]*Var, row int) Expr {
	newExpr := NewExpr(0)
	for col := 0; col < len(vs[0]); col++ {
		newExpr.Plus(vs[row][col])
	}
	return newExpr
}

// SumCol returns the sum of all variables in a single specified column of
// a variable matrix.
func SumCol(vs [][]*Var, col int) Expr {
	newExpr := NewExpr(0)
	for row := 0; row < len(vs); row++ {
		newExpr.Plus(vs[row][col])
	}
	return newExpr
}

// Dot returns the dot product of a vector of variables and slice of floats.
func Dot(vs []*Var, coeffs []float64) Expr {
	if len(vs) != len(coeffs) {
		log.WithFields(log.Fields{
			"num_vars":   len(vs),
			"num_coeffs": len(coeffs),
		}).Panic("Number of vars and coeffs mismatch")
	}

	newExpr := NewExpr(0)
	for i := range vs {
		newExpr.Plus(vs[i].Mult(coeffs[i]))
	}

	return newExpr
}