# CoCoA:HowTo:Plot order ideals

At the CoCoA Summer School 2005 there was a discussion about the possibility to plot order ideals. An order ideal is simply the complement of an ideal's leading term ideal, it could be described as a vector space basis of the quotient space P/I consisting of monomials as well (this is exactly the B in Macaulay's Basis Theorem with respect to the notation of Kreuzer's & Robbiano's book).

The question was, if there is any software to visualize these order ideals for polynomial rings in two or three indeterminants. During the school, Anna Bigatti and Daniel Heldt developed tools to plot order ideals.

These tools use CoCoa 4 and either POV-Ray or Latex. The code uses CoCoA's QuotientBasis command, to get a list of all terms to draw and than draws these terms (or selects which of them should be drawn and which are invisible, in case of the latex pictures).

The code to plot the order ideals is given in the next sections:

## CoCoA & Latex Code (1. Version)

Both functions (this and the next one) get a zero-dimensional ideal as input. The output is some text, containing the latex picture enviroment. Simply render this to get a picture of your order ideal. You can even change the point of view of the model, by changing V1, V2, V3 and L1, L2, L3. How this exactly works can be figured out quite easily by having a look at a documentation for the latex picture enviroment.

 Define BorderTeX(I)
String:='\begin{picture}(300,300)';

Offset := Vector(150,150);
V1 := Vector(-1,-1);
V2 := Vector(0,1);
V3 := Vector(1,0);
L1 := 14;
L2 := 20;
L3 := 20;

// get the Vectorspace-Basis of P/I:

B := QuotientBasis(I);

// check what to paint for what Basis Element:

// Check for all Elements in Basis what to draw:
ForEach El_B In B Do
L := Log(El_B);
Start := Offset + L1*L[1]*V1 + L2*L[2]V2 + L3*L[3]*V3;

If Not(Indet(1)*Indet(2)*El_B IsIn B) And L[3] > 0 Then
Line := '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\line('+Sprint(-V3[1])+','+Sprint(-V3[2])+'){'+Sprint(L3)+'}}';
String := String + Line;
EndIf;
If Not(Indet(1)*Indet(3)*El_B IsIn B) And L[2] > 0 Then
Line := '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\line('+Sprint(-V2[1])+','+Sprint(-V2[2])+'){'+Sprint(L2)+'}}';
String := String + Line;
EndIf;
If Not(Indet(2)*Indet(3)*El_B IsIn B) And L[1] > 0 Then
Line := '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\line('+Sprint(-V1[1])+','+Sprint(-V1[2])+'){'+Sprint(L1)+'}}';
String := String + Line;
EndIf;

EndForEach;

Return String+'\end{picture}';
EndDefine;


code by dheldt 08:37, 22 Jun 2005 (CEST)

## CoCoA & Latex Code (2. Version)

I created another version, a little bit more sophisticated. It contains coordinate axes and scales the picture environment to the right size. The code for this is:

 Define Border(I)

//////////////////////////////////////////////////////////////////////////////
Offset := Vector(150,150);
V1 := Vector(-1,-1);    L1 := 14;
V2 := Vector(0,1);   L2 := 20;
V3 := Vector(1,0);   L3 := 20;

Max1 := 0;
Max2 := 0;
Max3 := 0;

//////////////////////////////////////////////////////////////////////////////
// get the Vectorspace-Basis of P/I:
B := QuotientBasis(I);

//////////////////////////////////////////////////////////////////////////////
// Compute picture's size:
ForEach El_B In B Do
L := Log(El_B);
If L[1] > Max1 Then Max1 := L[1]; EndIf;
If L[2] > Max2 Then Max2 := L[2]; EndIf;
If L[3] > Max3 Then Max3 := L[3]; EndIf;
EndForEach;

Max1:= Max1 + 1; Max2 := Max2 +1; Max3 := Max3 +1;

Width  := Sum([ Abs(LC((Max1+3)*L1*V1[1])),Abs(LC((Max2+3)*L2*V2[1])),Abs(LC((Max3+3)*L3*V3[1])) ]);
Height := Sum([ Abs(LC((Max1+3)*L1*V1[2])),Abs(LC((Max2+3)*L2*V2[2])),Abs(LC((Max3+3)*L3*V3[2])) ]);

String:='\begin{picture}('+Sprint(Width)+','+Sprint(Height)+')';

//////////////////////////////////////////////////////////////////////////////
// Compute Offset / (0,0,0):
Offset:=Vector(Abs(Min([ LC((Max1+3)*L1*V1[1]),LC((Max2+3)*L2*V2[1]),LC((Max3+3)*L3*V3[1])])),
Abs(Min([ LC((Max1+3)*L1*V1[2]),LC((Max2+3)*L2*V2[2]),LC((Max3+3)*L3*V3[2])])));

//////////////////////////////////////////////////////////////////////////////
// Check for all Elements in Basis what to draw:
ForEach El_B In B Do
L := Log(El_B);
Start := Offset + L1*L[1]*V1 + L2*L[2]V2 + L3*L[3]*V3;

If Not(Indet(1)*Indet(2)*El_B IsIn B) And L[3] > 0 Then
Line := '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\line('+Sprint(-V3[1])+','+Sprint(-V3[2])+'){'+Sprint(L3)+'}}';
String := String + Line;
EndIf;
If Not(Indet(1)*Indet(3)*El_B IsIn B) And L[2] > 0 Then
Line := '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\line('+Sprint(-V2[1])+','+Sprint(-V2[2])+'){'+Sprint(L2)+'}}';
String := String + Line;
EndIf;
If Not(Indet(2)*Indet(3)*El_B IsIn B) And L[1] > 0 Then
Line := '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\line('+Sprint(-V1[1])+','+Sprint(-V1[2])+'){'+Sprint(L1)+'}}';
String := String + Line;
EndIf;
EndForEach;

//////////////////////////////////////////////////////////////////////////////
// Draw the three axis and the indeterminates names:

Start := Offset + Max1 * V1 * L1;
String := String + '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\vector('+Sprint(V1[1])+','+Sprint(V1[2])+'){'+Sprint(2*L1)+'}}';

String := String + '\put('+Sprint(Start[1]+3*L1*V1[1])+','+Sprint(Start[2]+3*L1*V1[2])+')
{$\displaystyle ' +Sprint(Indet(1))+'$}';

Start := Offset + Max2 * V2 * L2;
String := String + '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\vector('+Sprint(V2[1])+','+Sprint(V2[2])+'){'+Sprint(2*L2)+'}}';

String := String + '\put('+Sprint(Start[1]+3*L2*V2[1])+','+Sprint(Start[2]+3*L2*V2[2])+')
{$\displaystyle ' +Sprint(Indet(2))+'$}';

Start := Offset + Max3 * V3 * L3;
String := String + '\put('+Sprint(Start[1])+','+Sprint(Start[2])+')
{\vector('+Sprint(V3[1])+','+Sprint(V3[2])+'){'+Sprint(2*L3)+'}}';

String := String + '\put('+Sprint(Start[1]+3*L3*V3[1])+','+Sprint(Start[2]+3*L3*V3[2])+')
{$\displaystyle ' +Sprint(Indet(3))+'$}';

Return String+'\end{picture}';
EndDefine;


code by dheldt, 22 Jun 2005 (CEST)

## Latex Framework

As a framework where to copy&paste the output to, you can use the following latex code:

 \documentclass[12pt,a4paper]{article}

\usepackage{umlaut,a4wide,amsmath,amssymb,stmaryrd,color,graphicx,fancyhdr,multicol}
\usepackage[latin1]{inputenc}
\setlength{\parindent}{0mm}

\begin{document}

% Copy output here!

\end{document}


code by dheldt, 22 Jun 2005 (CEST)

## CoCoA & POV-Ray Code

This function returns some POV-Ray code to plot the quotient ideal of the input ideal (not necessarily zero-dimensional). The output of QuotientBasisPOV should be saved into a file called "monomials.inc" (see the example below), in order to be included by QuotienBasis.pov:

 Define NewLine()
Return "
";
EndDefine; -- NewLine

Define QuotientBasisPOV(I)
If NumIndets()<>3 Then Error("QuotientBasisPOV: ring must have 3 indeterminates"); EndIf;
String := "";
GENS := Interreduced(Gens(I));
-----
XMax := Max([Deg(T, Indet(1)) | T In GENS]);
YMax := Max([Deg(T, Indet(2)) | T In GENS]);
ZMax := Max([Deg(T, Indet(3)) | T In GENS]);
XYZMax := Max(XMax, YMax, ZMax);
-----
String := String + "#declare CamZoom="
+ Sprint(100/Isqrt(XYZMax)) +";"
+ NewLine();
String := String + "#declare CamEye=<0,"
+ Sprint(ZMax/4) +",0>;"
+ NewLine();

-----
G1 := [Indet(1)^(XMax+1), Indet(2)^(YMax+1), Indet(3)^(ZMax+1)];
G2 := [G1[1]*Indet(1), G1[2]*Indet(2), G1[3]*Indet(3)];
--  G2 := [Indet(1)^(XYZMax+2), Indet(2)^(XYZMax+2), Indet(3)^(XYZMax+2)];
----- axes
String := String + "#declare AxisTags = union {" + NewLine();
Line := "object {object AxisTag(""x"") translate <"
+Sprint(XMax+3) + ",0,0.1> }" + NewLine();
String := String + Line;
Line := "object {object AxisTag(""y"") translate <0,"
+Sprint(YMax+3) + ",0.1> }" + NewLine();
String := String + Line;
Line := "object {object AxisTag(""z"") translate <0,0.1,"
+Sprint(ZMax+3) + "> }" + NewLine();
String := String + Line;
String :=  String + "}" + NewLine();
----- Generators
String := String + "#declare Generators = union {" + NewLine();
ForEach G In GENS Do
L := Log(G);
Line := "union { object{Generator} ";
String := String + Line;
Line := "object Exponents(""" +
+ Sprint(L[1]) + " " + Sprint(L[2]) + " " + Sprint(L[3])
+ """) translate <"
+Sprint(L[1]) + "," + Sprint(L[2]) + "," + Sprint(L[3])
+"> }" + NewLine();
String := String + Line;
EndForEach;
String :=  String + "}" + NewLine();
----- Monomials
B := QuotientBasis(I+Ideal(G1));
String := String + "#declare Monomials = union {" + NewLine();
ForEach El_B In B Do
L := Log(El_B);
Line := "object{ SolidCube() translate <"+
Sprint(L[1]) + "," + Sprint(L[2]) + "," + Sprint(L[3])
+"> }" + NewLine();
String := String + Line;
EndForEach;
String :=  String + "}" + NewLine();
---- InftyMonomials
B := Diff(QuotientBasis(I+Ideal(G2)), QuotientBasis(I+Ideal(G1)));
String := String + "#declare InftyMonomials = union {" + NewLine();
ForEach El_B In B Do
L := Log(El_B);
Line := "object{ SolidCube() translate <"+
Sprint(L[1]) + "," + Sprint(L[2]) + "," + Sprint(L[3])
+"> }" + NewLine();
String := String + Line;
EndForEach;
String :=  String + "}" + NewLine();
----
Return String;
EndDefine; -- QuotientBasisPOV

/*
-- EXAMPLE --
Use Q[x,y,z];

I := Ideal(x^10yz^6, x^7y^2z^3, xy^3z^4, x^3y^3z^3, xy^4z^4, y^6);
F := OpenOFile("/Users/bigatti/Desktop/POV-Anna/monomials.inc", "w");
PrintLn QuotientBasisPOV(I) On F;
*/


code by bigatti, 27 Jun 2005

## POV-Ray Framework

This is the file QuotientBasis.pov, which is including the file "monomials.inc" generated from the code above. You should run it with POV-Ray with antialiasing on.

 // Copyright (c) 2005  Anna Bigatti
// You are free to use any part of this example in your own programs.

// ------------------------------
#include "colors.inc"
#include "functions.inc"
#include "textures.inc"
#include "metals.inc"
#include "glass.inc"

global_settings{
max_trace_level 50
}

// ------------------------------
// Set settings
// ------------------------------
#declare CamLoc=<500,500,-500>;
#declare AspectRatio=4/3;

light_source{<500,400,-200> color White*5}
//plane{y,0 texture{pigment{rgbf <0.89, 0.98, 1.0, 0.95>}finish{F_Glass5}} hollow}

//------------------------------
// colours
//------------------------------
sky_sphere{ pigment{ color Gray90 } }

#declare P_X = rgbf <0.04, 0.25, 0, 0>;
#declare P_Y = rgbf <0.30, 0.35, 0, 0>;
#declare P_Z = rgbf <0.05, 0.05, 0.4, 0>;
#declare P_Cube =      rgbf <0.01, 0.01, .3, 0>;
#declare P_ClearCube = rgbf <0.4, 0.5, .6, .9>;
#declare P_Exponent =  rgbt <.2,1,.2,.0>;

#declare Generator =  sphere{0, .2 texture {T_Brass_2A} }

#declare Axes = union {
cylinder { <0, 0, 0>, <500, 0, 0>, 0.05 pigment {color P_X} }
cylinder { <0, 0, 0>, <0, 500, 0>, 0.05 pigment {color P_Y}  }
cylinder { <0, 0, 0>, <0, 0, 500>, 0.05 pigment {color P_Z}  }
}

// ------------------------------
// creates the cube
// ------------------------------
#macro SolidCube()
union{
#declare sB=0.48;
#declare rB=0.02;
union{
cylinder{-sB*x,sB*x,rB translate <0,sB,sB> pigment {color P_X}}
cylinder{-sB*x,sB*x,rB translate <0,-sB,sB> pigment {color P_X}}
cylinder{-sB*x,sB*x,rB translate <0,sB,-sB> pigment {color P_X}}
cylinder{-sB*x,sB*x,rB translate <0,-sB,-sB> pigment {color P_X}}
cylinder{-sB*y,sB*y,rB translate <sB,0,sB>  pigment {color P_Y}}
cylinder{-sB*y,sB*y,rB translate <sB,0,-sB> pigment {color P_Y}}
cylinder{-sB*y,sB*y,rB translate <-sB,0,sB> pigment {color P_Y}}
cylinder{-sB*y,sB*y,rB translate <-sB,0,-sB> pigment {color P_Y}}
cylinder{-sB*z,sB*z,rB translate <sB,sB,0> pigment {color P_Z}}
cylinder{-sB*z,sB*z,rB translate <sB,-sB,0> pigment {color P_Z}}
cylinder{-sB*z,sB*z,rB translate <-sB,sB,0> pigment {color P_Z}}
cylinder{-sB*z,sB*z,rB translate <-sB,-sB,0> pigment {color P_Z}}
sphere{0,rB translate <sB,sB,sB>}
sphere{0,rB translate <sB,sB,-sB>}
sphere{0,rB translate <sB,-sB,sB>}
sphere{0,rB translate <sB,-sB,-sB>}
sphere{0,rB translate <-sB,sB,sB>}
sphere{0,rB translate <-sB,sB,-sB>}
sphere{0,rB translate <-sB,-sB,sB>}
sphere{0,rB translate <-sB,-sB,-sB>}
}

box{-0.45,0.45 interior{ior 1.1} }

translate <sB-rB, sB-rB, sB-rB>
}
#end

#macro Exponents(Exp)
{text {
ttf "crystal.ttf",
Exp,
.03,
<-.1,0,0>
scale < .7, .7,.7>
matrix <
0, 1, 0.7,
0, 0, 0.7,
1, 0, 0,
.7, 0, 0.4>
pigment {color P_Exponent}
no_reflection
}}
#end

#macro AxisTag(Exp)
{text {
ttf "crystal.ttf",
Exp,
.03,
<-.1,0,0>
//  scale < .7, .7,.7>
matrix <
0, 1, 0.7,
0, 0, 0.7,
1, 0, 0,
0, 0, 0.1>
pigment {color Gray20}
no_reflection
}}
#end

// ------------------------------
// scene
// ------------------------------
#include "monomials.inc"     // place the cubes

camera {
location CamLoc
direction z*CamZoom
right x*AspectRatio
look_at CamEye
}

union{
object {Generators}
object {Axes}
object {AxisTags}
object {Monomials  texture{pigment{color P_Cube}}}
object {InftyMonomials  texture{pigment{color P_ClearCube}}}
matrix <
0, 0, -1,
1, 0, 0,
0, 1, 0,
0, 0, 0
>

}


code by bigatti, 27 Jun 2005

## POV-Ray Plots

This image is the POV-Ray output for a zero-dimensional ideal: the brass balls are the generators of the leading term ideal. File:QuotientBasis2.png

This image is the POV-Ray output for a non zero-dimensional ideal: the transparent blocks indicate that the "staircase" is not limited. File:QuotientBasis1.png