- See Also
- Average
- Binomial coefficient
- Cross-sum of non-negative integers
- Epsilon
- Factorial
- Fibonacci numbers
- Integer Check
- Integer maximum
- Linear regression and correlation coefficient
- Logarithm to any base
- Logarithm to Base Two
- Maximum and minimum
- Means of a number list: arithmetic, geometric, quadratic, harmonic
- Mid
- Numerical functions for [expr]
- Prime factors of an integer
- Random Numbers
- Square Mean and Standard Deviation
- Sign of a number
- Traditional degrees

- math module in tcllib
- tcl::mathfunc
- integrate
- Stats
- converting between rectangular and polar co-ordinates
- Fraction math - Complex math made simple (Complex numbers)
- Sample Math Programs
- Binomial coefficients - including the gamma function.
- Combinatorial mathematics functions
- A set of Set operations
- Fast Fourier Transform
- Multivariate Linear Regression
- Mathematically oriented extensions
- pi
- Taking the Nth power

arithmetic mean of a list of numbers:

proc average L { expr ([join $L +])/[llength $L]. }

Note that empty lists produce a syntax error. The dot behind llength casts it to double (not dangerous here, as llength will always return a non-negative integer) -- *RS*

Perhaps the **best** (what criteria?) should move to the Binomial page and just a pointer to the page should be here? (This got too long; I'm keeping the best algorithm here, moving the previous discussion to Binomial Coefficients. This solution is called *binom3* in that page.)

proc binom {m n} { set n [expr {(($m-$n) > $n) ? $m-$n : $n}] if {$n > $m} {return 0} if {$n == $m} {return 1} set res 1 set d 0 while {$n < $m} { set res [expr {($res*[incr n])/[incr d]}] } set res }

proc crosssum {x} {expr [join [split $x ""] +]}

Note that this expression may not be braced. (RS)

Comparing two floats x,y for equality is most safely done by testing *abs($x-$y)<$eps*, where eps is a sufficiently small number. You can find out which *eps* is good for your machine with the following code:

proc eps {{base 1}} { set eps 1e-20 while {$base-$eps==$base} { set eps [expr {$eps+1e-22}] } set eps [expr {$eps+1e-22}] } % eps 1 5.55112000002e-017 ;# on both my Win2K/P3 and Sun/Solaris % eps 0.1 6.93889999999e-018 % eps 0.01 8.674e-019 % eps 0.001 1.085e-019

RS 2008-01-02: Here's a little example for a user-defined recursive factorial function:

proc tcl::mathfunc::fac x { expr {$x<2? 1: $x*fac($x-1)} } expr fac(5) # 120

I see a factorial function on 3-4 different pages -some not even about math. And yet none in the tcllib math library. Perhaps one should be submitted. How to determine *best*?

KBK: There is indeed a factorial in ::tcllib::math. It's in some sense 'better' than any of the ones I've seen here on the Wiki:

- It returns
*exact*results for factorial x, where x is an integer and 0<=x<=21. - It returns floating point results for integer x, 22<=x<=170, that are correct to 1 unit in the least significant bit position.
- It returns approximate results, precise to nine significant digits, for all other
*real*x, x>=0, by using the identity x! = Gamma( x + 1 ). In particular, this precision has been exhaustively verified for all half-integer arguments that give results within the range of IEEE floating point. - It has companion functions for binomial coefficients, the Gamma function and the Beta distribution that are as precise as it is. Moreover, these functions do
*not*suffer from premature overflow; they perform well with large arguments: [choose 10000 100] doesn't give the function heartburn.

RS I like this one, compact but recursive:

proc fac n { expr {$n<2? 1: $n*[fac [expr {$n-1}]]} }

However, this one runs 1/3 faster:

proc fac2 n { expr $n<2? 1: [join [iota 1 $n] *]+0 }

given an index generator *iota*, e.g. *iota 1 5 => {1 2 3 4 5}*

proc iota {base n} { set res {} for {set i $base} {$i<$n+$base} {incr i} {lappend res $i} set res }

However, factorials computed in terms of expr are correct only until 12!; above that you get "false positives", negatives, or zeroes.. Of course one could use doubles, which seem to be exact up to 18! (at the maximum tcl_precision 17). But the fastest *fac* is still tabulated:

proc fac3 n { lindex { 1 1 2 6 24 120 720 5040 40320 362880 3628800 39916800 479001600 479001600.0 87178291200.0 1307674368000.0 20922789888000.0 355687428096000.0 6402373705728000.0 } $n } ;#-)

tcllib::math has an iterative version, but here's the "closed form" if anyone cares:

proc fib n { expr {round(1/sqrt(5)*(pow((1+sqrt(5))/2,$n) - (pow((1-sqrt(5))/2,$n))))} } ;# RS

Lars H: Actually, you don't need to compute the second term, since it always contributes < 1/2 for non-negative *n*. You can simply do

proc fib2 n { expr {round(1/sqrt(5)*pow((1+sqrt(5))/2,$n))} }

For negative *n* it is instead the first term that can be ignored, but one rarely needs those Fibonacci numbers.

BTW, I also changed an "int" to a "round" in RS's proc (if you're unlucky with the numerics, "int" can give you one less than the correct answer).

see whether variable has an integer value

Since Tcl 8.1.1, the built-in *string is int* does the same for a value.

proc is_int x { expr {![catch {incr x 0}]} } proc is_no_int x { catch {incr x 0} }

(MAXINT): determine biggest positive signed integer (by Jeffrey Hobbs):

proc largest_int {} { set int 1 set exp 7; # assume we get at least 8 bits while {$int > 0} { set int [expr {1 << [incr exp]}] } expr {$int-1} }

proc reg,cor points { # linear regression y=ax+b for {{x0 y0} {x1 y1}...} # returns {a b r}, where r: correlation coefficient foreach i {N Sx Sy Sxy Sx2 Sy2} {set $i 0.0} foreach point $points { foreach {x y} $point break set Sx [expr {$Sx + $x}] set Sy [expr {$Sy + $y}] set Sx2 [expr {$Sx2 + $x*$x}] set Sy2 [expr {$Sy2 + $y*$y}] set Sxy [expr {$Sxy + $x*$y}] incr N } set t1 [expr {$N*$Sxy - $Sx*$Sy}] set t2 [expr {$N*$Sx2 - $Sx*$Sx}] set a [expr {double($t1)/$t2}] set b [expr {double($Sy-$a*$Sx)/$N}] set r [expr {$t1/(sqrt($t2)*sqrt($N*$Sy2-$Sy*$Sy))}] list $a $b $r } ;#RS

proc log {base x} { expr {log($x)/log($base)} } ;# RS

proc ld x "expr {log(\$x)/[expr log(2)]}"

This is an example of a "live" proc body - the divisor is computed only once, at definition time. With a single backslash escape needed, it's worth the fun ;-) (RS)

proc max {a args} { foreach i $args {if {$i>$a} {set a $i}};return $a } proc min {a args} { foreach i $args {if {$i<$a} {set a $i}};return $a }

Works with whatever < and > can compare (strings included). Or how about (float numbers only):

proc max args { lindex [lsort -real $args] end } proc min args { lindex [lsort -real $args] 0 }

Or, use -dictionary to handle strings, ints, real.... and also allow to be called with a single list arg (FYI, it's actually a bit faster to use the sort method)

proc min args { if {[llength $args] == 1} {set args [lindex $args 0]} lindex [lsort -dict $args] 0 } proc max args { if {[llength $args] == 1} {set args [lindex $args 0]} lindex [lsort -dict $args] end }

RS: ... only that you get lsort results like

{-1 -5 -10 0 5 10}

if you use the **-dict** mode of lsort. Numeric max/min should rather use -integer or -float. Max/min of strings must be left to dedicated procs, if ever needed.

Should this function move to the Stats page?

proc mean L { expr ([join $L +])/[llength $L]. } proc gmean L { expr pow([join $L *],1./[llength $L]) } proc qmean L { expr sqrt((pow([join $L ,2)+pow(],2))/[llength $L]) } proc hmean L { expr [llength $L]/(1./[join $L +1./]) }

where *qmean* is the best braintwister... For a list of {1 2} the string

sqrt((pow( 1 ,2)+pow( 2 ,2))/ 2)

(blanks added for clarity) is built up and fed to *expr*, where it makes a perfectly well-formed expression if not braced. (RS)

proc median L {lindex $L [expr {[llength $L]/2}] } ;# DKF

JPS: That median assumes the list is already sorted. This one doesn't:

proc median {l} { if {[set len [llength $l]] % 2} then { return [lindex [lsort -real $l] [expr {($len - 1) / 2}]] } else { return [expr {([lindex [set sl [lsort -real $l]] [expr {($len / 2) - 1}]] \ + [lindex $sl [expr {$len / 2}]]) / 2.0}] } }

AMG: Here's a math function I sometimes find useful. It accepts three arguments, and it returns whichever of the three is between the other two. It's mostly useful to clamp a number to a range.

proc ::tcl::mathfunc::mid {a b c} { lindex [lsort -real [list $a $b $c]] 1 }

It can also be implemented as a bunch of [if]s, which is how I do it in C.

Here is one *incorrect* implementation you should watch out for:

proc ::tcl::mathfunc::mid {a b c} { expr {max($a, min($b, $c))} }

This is what Allegro (include/allegro/base.h) has used since the dawn of time. :^( I'm reporting it now; hopefully it'll be fixed. If you're curious, see [1 ] for my writeup.

KPV The folk algorithm for finding the middle number (or second highest in a longer list) is to take the max of the pair-wise mins. To wit:

max(min($a,$b), min($a,$c), min($b,$c))

LV So what is an example of a case in which the second, *incorrect*, version of the algorithm fails? Answer: "incorrect_mid 1 0 0" returns 1. The problem is it doesn't (always) handle the case where two of the inputs are the same. Doh.

AMG: I thought the problem was that it doesn't handle the case of the first input being greater than the other two. This wasn't a problem for Allegro because everyone used its MID macro thus: **MID(minimum_value, value_to_clamp, maximum_value)**.

CritLib (see the Critcl page) now includes an adapted version of Donal K. Fellows' extension which lets you write numerical functions for "expr" in Tcl. See the "mathf" readme [2 ] - JCW

proc primefactors n { # a number x is prime if [llength [primefactors $x]]==1 set res {} set f 2 while {$f<=$n} { while {$n%$f==0} { set n [expr {$n/$f}] lappend res $f } set f [expr {$f+2-($f==2)}] } set res } ;#RS

Of course, since 8.0 just say

expr {rand()}

Jeffrey Hobbs has this substitute for pre-8.0 Tcl:

set _ran [clock seconds] proc random {range} { global _ran set _ran [expr ($_ran * 9301 + 49297) % 233280] return [expr int($range * ($_ran / double(233280)))] }

Pass in an int and it returns a number (0..int). Also, the Wiki page on "rand" has more on the subject.

Perhaps this function should move to the Stats page mentioned above? **Square mean and standard deviation**:

proc mean2 list { set sum 0 foreach i $list {set sum [expr {$sum+$i*$i}]} expr {double($sum)/[llength $list]} } proc stddev list { set m [mean $list] ;# see below for [mean] expr {sqrt([mean2 $list]-$m*$m)} } ;# RS

proc sgn {a} {expr {$a>0 ? 1 : $a<0 ? -1 : 0}} ;# rmax proc sgn x {expr {$x<0? -1: $x>0}} ;# RS proc sgn x {expr {($x>0)+($x>>31)}} ;# jcw (32-bit arch) proc sgn x {expr {($x>0)-($x<0)}} ;# rmax again

Actually,

string compare $a 0

seems to give the correct result for all integer values and floating point values not equal to 0.

0.0 (and 0.00 etc) [string compare 0.0 0] returns 1, however.

sergiol: I was playing codegolf and based on the C answer http://codegolf.stackexchange.com/a/103831/29325 I confirmed it on tcl

puts [expr !!$n|$n>>31]

can be seen on: http://rextester.com/live/BKGZ8868

*clock format* can be put to un-timely uses. As degrees especially in geography are also subdivided in minutes and seconds, how's this one-liner for formatting decimal degrees:

proc dec2deg x { concat [expr int($x)] [clock format [expr round($x*3600)] -format "%M' %S\""] }

An additional *-gmt 1* switch is needed if you happen to live in a non-integer timezone. (RS)