proc phi {i1 i2 i3 i4 fi} {
	set PI 3.14159265358979323846
	set atoms [atomselect top "index $i1 $i2 $i3 $i4" frame $fi]
	set positions [$atoms get {x y z}]
	set rA [lindex $positions 0]
	set rB [lindex $positions 1]
	set rC [lindex $positions 2]
	set rD [lindex $positions 3]
	set one [expr -[vecdot [veccross [vecsub $rA $rB] [vecsub $rB $rC]] [veccross [vecsub $rB $rC] [vecsub $rC $rD]]] / ([veclength [veccross [vecsub $rA $rB] [vecsub $rB $rC]]] * [veclength [veccross [vecsub $rB $rC] [vecsub $rC $rD]]])]
	if {$one > 1.0 || $one < -1.0} {
		set one [expr $one / $one]
	}
	set phi [expr acos($one) * 180 / $PI - 180]
	return [list $phi]
}

proc allphi {i1 i2 i3 i4 i5} {
	set nf [molinfo top get numframes]
	set outfile [open angles.txt w]
	puts $outfile "ith phi psi"
	for {set i 0} {$i < $nf} {incr i} {
		set A1 [phi $i1 $i2 $i3 $i4 $i]
		set A2 [phi $i2 $i3 $i4 $i5 $i]
		puts $outfile "$i $A1 $A2"
	}
	close $outfile
}