proc math::combined_market_rate { args} {
    set sum 0.
    set N [llength $args]
    #puts "Debug: llength is $N of $args"
    if { $N == 0 } { return 0 }
    #puts "Line: "#__LINE__
    if {[lindex $args 0] == 0} {return 0}
    # if { ($N == 1) || ([lindex $args 0 ] == 0) } { return 0 }
    #puts "Line: "#__LINE__
    foreach val $args {
        # puts "Debug: adding $val"
        #set sum [ expr { $sum + 1.0/$val } ]
        += sum [/ 1.0 $val]
    }
    set combined_market_rate1 [ expr { 1.0/($sum/$N) } ]
    return $combined_market_rate1
}

puts " [ ::math::combined_market_rate 0.5524 0.4807 0.42918 0.47846 ] (Answer 0.40131)"
# various testcases
#puts [::math::combined_market_rate 0.5524 0.4807 0.42918 0.47846 ]
assert [::math::combined_market_rate 0.5524 0.4807 0.42918 0.47846 ] {== [round $_ 5] 0.48131} -v -line #__LINE__
# answer 0.48131 "
#puts [ ::math::combined_market_rate .1 .2 .3 .4 ]
assert [::math::combined_market_rate .1 .2 .3 .4 ] {== [round $_ 3] 0.192} -v -line #__LINE__
# answer
#::math::combined_market_rate -.1 -.2 -.3 -.4 #answer -0.192
assert [::math::combined_market_rate -.1 -.2 -.3 -.4 ] {== [round $_ 3] -0.192} -v -line #__LINE__
# check [/ 1. [/ [+ [/ 1. -.1] [/ 1. -.2] [/ 1. -0.3 ] [/ 1. -0.4] ] 4. ] ]
#returns -0.192
#puts " [ ::math::combined_market_rate .1 ] "
#:math::combined_market_rate -.1 -.2 .3 .4 #answer -0.4363636363636364
assert [::math::combined_market_rate -.1 -.2 .3 .4 ] {== [round $_ 6] -0.436364} -v -line #__LINE__

#set check [/ 1. [/ [+ [/ 1. -.1] [/ 1. -.2] [/ 1. 0.3 ] [/ 1. 0.4] ] 4. ] ]
# check equals -0.4363636363636364

# ::math::combined_market_rate # null returns zero, correct.
assert [::math::combined_market_rate] {== $_ 0} -v -line #__LINE__
# ::math::combined_market_rate 0 # arg 0 returns zero, correct.
assert [::math::combined_market_rate 0] {== $_ 0} -v -line #__LINE__
#puts " for (::math::combined_market_rates .1) returns .1 "
assert [::math::combined_market_rate .1 ] {== $_ 0.1} -v -line #__LINE__