Added poly and numeric modules

1 files changed, 411 insertions, 0 deletions

diff --git a/lib/pure/poly.nim b/lib/pure/poly.nim
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+#
+#
+#            Nimrod's Runtime Library
+#        (c) Copyright 2013 Robert Persson
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+import math
+import strutils
+import numeric
+
+
+type 
+    TPoly* = object
+        cofs:seq[float]
+
+  
+proc initPolyFromDegree(n:int):TPoly=
+  ## internal usage only
+  ## caller must initialize coefficients of poly
+  ## and possibly  `clean` away zero exponents
+  var numcof=n+1   #num. coefficients is one more than degree
+  result.cofs=newSeq[float](numcof)
+  
+proc degree*(p:TPoly):int=
+  ## Returns the degree of the polynomial,
+  ## that is the number of coefficients-1
+  return p.cofs.len-1
+
+
+proc eval*(p:TPoly,x:float):float=
+  ## Evaluates a polynomial function value for `x`
+  ## quickly using Horners method
+  var n=p.degree
+  result=p.cofs[n]
+  dec n
+  while n>=0:
+    result = result*x+p.cofs[n]
+    dec n
+
+proc `[]` *(p:TPoly;idx:int):float=
+  ## Gets a coefficient of the polynomial.
+  ## p[2] will returns the quadric term, p[3] the cubic etc.
+  ## Out of bounds index will return 0.0.
+  if idx<0 or idx>p.degree:
+      return 0.0
+  return p.cofs[idx]
+    
+proc `[]=` *(p:var TPoly;idx:int,v:float)=
+  ## Sets an coefficient of the polynomial by index.
+  ## p[2] set the quadric term, p[3] the cubic etc.
+  ## If index is out of range for the coefficients,
+  ## the polynomial grows to the smallest needed degree.
+  if idx<0: 
+    return
+
+  if idx>p.degree:  #polynomial must grow
+    echo("GROW!")
+    var oldlen=p.cofs.len
+    p.cofs.setLen(idx+1)
+    for q in oldlen.. <high(p.cofs):
+      p.cofs[q]=0.0 #new-grown coefficients set to zero
+
+  p.cofs[idx]=v
+    
+      
+iterator coefficients*(p:TPoly):float=
+  ## Iterates through the corfficients of the polynomial.
+  var i=p.degree
+  while i>=0:
+    yield p[i]
+    dec i    
+    
+proc clean*(p:var TPoly;zerotol=0.0)=
+  ## Removes leading zero coefficients of the polynomial.
+  ## An optional tolerance can be given for what's considered zero.
+  var n=p.degree
+  var relen=false
+
+  while n>0 and abs(p[n])<=zerotol:    # >0 => keep at least one coefficient
+    dec n
+    relen=true
+
+  if relen: p.cofs.setLen(n+1)
+
+
+proc `$` *(p:TPoly):string = 
+  ## Gets a somewhat reasonable string representation of the polynomial
+  ## The format should be compatible with most online function plotters,
+  ## for example directly in google search
+  result=""
+  var first=true #might skip + sign if first coefficient
+  
+  for idx in countdown(p.degree,0):
+    var a=p[idx]
+    
+    if a==0.0:
+      continue
+    
+    if a>= 0.0 and not first:
+      result.add('+')
+    first=false
+
+    if a!=1.0 or idx==0:
+      result=result & formatFloat(a,ffDefault,0)
+    if idx>=2:
+      result.add("x^" & $idx)
+    elif idx==1:
+      result.add("x")
+
+  if result=="":
+      result="0"
+          
+
+proc derivative*(p:TPoly):TPoly=
+  ## Returns a new polynomial, which is the derivative of `p`
+  newSeq[float](result.cofs,p.degree)
+  for idx in 0..high(result.cofs):
+    result.cofs[idx]=p.cofs[idx+1]*float(idx+1)
+    
+proc diff*(p:TPoly,x:float):float=
+  ## Evaluates the differentiation of a polynomial with
+  ## respect to `x` quickly using a modifed Horners method
+  var n=p.degree
+  result=p[n]*float(n)
+  dec n
+  while n>=1:
+    result = result*x+p[n]*float(n)
+    dec n
+
+proc integral*(p:TPoly):TPoly=
+  ## Returns a new polynomial which is the indefinite
+  ## integral of `p`. The constant term is set to 0.0
+  result=initPolyFromDegree(p.degree+1)
+  result.cofs[0]=0.0  #constant arbitrary term, use 0.0
+  for i in 1..high(result.cofs):
+    result.cofs[i]=p.cofs[i-1]/float(i)
+        
+
+proc integrate*(p:TPoly;xmin,xmax:float):float=
+  ## Computes the definite integral of `p` between `xmin` and `xmax`
+  # TODO: this can be done faster using a modified horners method,
+  # see 'diff' function above.
+  var igr=p.integral
+  result=igr.eval(xmax)-igr.eval(xmin)
+
+proc initPoly*(cofs:varargs[float]):TPoly=
+  ## Initializes a polynomial with given coefficients.
+  ## The most significant coefficient is first, so to create x^2-2x+3:
+  ## intiPoly(1.0,-2.0,3.0)
+  if len(cofs)<=0:
+      result.cofs= @[0.0]  #need at least one coefficient
+  else:
+    # reverse order of coefficients so indexing matches degree of
+    # coefficient...
+    result.cofs= @[]
+    for idx in countdown(cofs.len-1,0):  
+      result.cofs.add(cofs[idx])
+
+  result.clean #remove leading zero terms
+
+
+proc divMod*(p,d:TPoly;q,r:var TPoly)=
+  ## Divides `p` with `d`, and stores the quotinent in `q` and
+  ## the remainder in `d`
+  var 
+    pdeg=p.degree
+    ddeg=d.degree
+    power=p.degree-d.degree
+    ratio:float
+  
+  if power<0: #denominator is larger than numerator
+    q=initPoly(0.0) #division result is 0
+    r=p #remainder is numerator
+    return 
+      
+  q=initPolyFromDegree(power)
+  r=p
+  
+  for i in countdown(pdeg,ddeg):
+    ratio=r[i]/d[ddeg]
+    
+    q[i-ddeg]=ratio
+    r[i]=0.0
+    
+    for j in countup(0,<ddeg):
+        var idx=i-ddeg+j
+        r[idx] = r[idx] - d[j]*ratio
+     
+  r.clean # drop zero coefficients in remainder
+ 
+
+        
+proc `+` *(p1:TPoly,p2:TPoly):TPoly=
+  ## Adds two polynomials
+  var n=max(p1.cofs.len,p2.cofs.len)
+  newSeq(result.cofs,n)
+  
+  for idx in countup(0,n-1):
+      result[idx]=p1[idx]+p2[idx]
+      
+  result.clean # drop zero coefficients in remainder
+    
+proc `*` *(p1:TPoly,p2:TPoly):TPoly=
+  ## Multiplies the polynomial `p1` with `p2`
+  var 
+    d1=p1.degree
+    d2=p2.degree
+    n=d1+d2
+    idx:int
+      
+  newSeq(result.cofs,n)
+
+  for i1 in countup(0,d1):
+    for i2 in countup(0,d2):
+      idx=i1+i2
+      result[idx]=result[idx]+p1[i1]*p2[i2]
+
+  result.clean
+
+proc `*` *(p:TPoly,f:float):TPoly=
+  ## Multiplies the polynomial `p` with a real number
+  result=initPolyFromDegree(p.degree)
+  for i in 0..high(p.cofs):
+    result[i]=p.cofs[i]*f
+  result.clean
+  
+proc `*` *(f:float,p:TPoly):TPoly=
+  ## Multiplies a real number with a polynomial
+  return p*f
+    
+proc `-`*(p:TPoly):TPoly=
+  ## Negates a polynomial
+  result=p
+  for i in countup(0,<result.cofs.len):
+    result.cofs[i]= -result.cofs[i]
+    
+proc `-` *(p1:TPoly,p2:TPoly):TPoly=
+  ## Subtract `p1` with `p2`
+  var n=max(p1.cofs.len,p2.cofs.len)
+  newSeq(result.cofs,n)
+  
+  for idx in countup(0,n-1):
+      result[idx]=p1[idx]-p2[idx]
+      
+  result.clean # drop zero coefficients in remainder
+    
+proc `/`*(p:TPoly,f:float):TPoly=
+  ## Divides polynomial `p`with real number `f`
+  result=initPolyFromDegree(p.degree)
+  for i in 0..high(p.cofs):
+    result[i]=p.cofs[i]/f
+  result.clean
+  
+proc `/` *(p,q:TPoly):TPoly=
+  ## Divides polynomial `p` with polynomial `q`
+  var dummy:TPoly
+  p.divMod(q,result,dummy)  
+
+proc `mod` *(p,q:TPoly):TPoly=
+  ## computes the polynomial modulo operation,
+  ## that is the remainder op `p`/`q`
+  var dummy:TPoly
+  p.divMod(q,dummy,result)
+
+
+proc normalize*(p:var TPoly)=
+  ## Multiplies the polynomial inplace by a term so that
+  ## the leading term is 1.0.
+  ## This might lead to an unstable polynomial
+  ## if the leading term is zero.
+  p=p/p[p.degree]
+
+
+proc solveQuadric*(a,b,c:float;zerotol=0.0):seq[float]=
+  ## Solves the quadric equation `ax^2+bx+c`, with a possible
+  ## tolerance `zerotol` to find roots of curves just 'touching'
+  ## the x axis. Returns sequence with 1 or 2 solutions, or nil
+  ## in case of no real solution.
+  result=nil
+  
+  var p,q,d:float
+  
+  p=b/(2.0*a)
+  
+  if p==inf or p==neginf: #linear equation..
+    var linrt= -c/b
+    if linrt==inf or linrt==neginf: #constant only
+      return nil
+    return @[linrt]
+  
+  q=c/a
+  d=p*p-q
+  
+  if d<0.0:
+    #check for inside zerotol range for neg. roots
+    var err=a*p*p-b*p+c #evaluate error at parabola center axis
+    if(err<=zerotol): return @[-p]
+    return nil
+  else:
+    var sr=sqrt(d)
+    result= @[-sr-p,sr-p]
+
+proc getRangeForRoots(p:TPoly;xmin,xmax:var float)=
+  ## helper function for `roots` function
+  ## quickly computes a range, guaranteed to contain
+  ## all the real roots of the polynomial
+  # see http://www.mathsisfun.com/algebra/polynomials-bounds-zeros.html
+
+  var deg=p.degree
+  var d=p[deg]
+  var bound1,bound2:float
+  
+  for i in countup(0,deg):
+      var c=abs(p.cofs[i]/d)
+      bound1=max(bound1,c+1.0)
+      bound2=bound2+c
+      
+  bound2=max(1.0,bound2)
+  xmax=min(bound1,bound2)
+  xmin= -xmax
+
+
+proc addRoot(p:TPoly,res:var seq[float],xp0,xp1,tol,zerotol,mergetol:float)=
+  ## helper function for `roots` function
+  ## try to do a numeric search for a single root in range xp0-xp1,
+  ## adding it to `res` (allocating `res` if nil)
+  var rootx,rooty:float
+  
+  if brent(xp0,xp1, proc(x:float):float=p.eval(x),rootx,rooty,tol):
+    if res==nil: res= @[rootx]
+    elif rootx>=res[high(res)]+mergetol: res.add(rootx) #dont add equal roots.
+  else:
+    #this might be a 'touching' case, check function value against
+    #zero tolerance
+    if abs(rooty)<=zerotol:
+      if res==nil: res= @[rootx]
+      elif rootx>=res[high(res)]+mergetol: res.add(rootx) #dont add equal roots.
+
+
+proc roots*(p:TPoly,tol=1.0e-9,zerotol=1.0e-6,mergetol=1.0e-12):seq[float]=
+  ## Computes the real roots of the polynomial `p`
+  ## `tol` is the tolerance use to break searching for each root when reached.
+  ## `zerotol` is the tolerance, which is 'close enough' to zero to be considered a root
+  ## and is used to find roots for curves that only 'touch' the x-axis.
+  ## `mergetol` is the tolerance, of which two x-values are considered beeing the same root.
+  ## Returns a sequence with the solutions, or nil in case of no solutions.
+  var deg=p.degree
+  var res:seq[float]=nil
+  if deg<=0:
+    return nil
+  elif p.degree==1:
+    var linrt= -p.cofs[0]/p.cofs[1]
+    if linrt==inf or linrt==neginf:
+      return nil #constant only => no roots
+    return @[linrt]
+  elif p.degree==2:
+    return solveQuadric(p.cofs[2],p.cofs[1],p.cofs[0],zerotol)
+  else:
+    # degree >=3 , find min/max points of polynomial with recursive
+    # derivative and do a numerical search for root between each min/max
+    var x0,x1:float
+    p.getRangeForRoots(x0,x1)
+    var minmax=p.derivative.roots(tol,zerotol,mergetol)
+    if minmax!=nil: #ie. we have minimas/maximas in this function
+      for x in minmax.items:
+        addRoot(p,res,x0,x,tol,zerotol,mergetol)
+        x0=x
+    addRoot(p,res,x0,x1,tol,zerotol,mergetol)
+
+  return res
+
+when isMainModule:
+  var ply=initPoly(1.0,-6.0,5.0,2.0)
+  var ply2 =initPoly(4.0,5.0,6.0)
+  
+  echo ply
+  echo ply2 
+  echo ply2-ply
+  
+  
+  
+  
+  var rts=ply.roots
+  if rts!=nil:
+    for i in rts:
+      echo formatFloat(i,ffDefault,0)
+  
+
+  discard readLine(stdin) 
+  
+  
+    
+  
+  
+    
+    
+    
+    
+    
+    
+    
+    
+    
+    
+        
+        
+        
+    
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