Image:Pythagoras.png

Produced by user Trainspotter using a program he wrote in the IDL language.

Program is listed below in case a modified version needs to be produced. (Program below is public domain, but IDL package itself is payware.)

 a=100. ; side A
 b=70.  ; side B
 m=3.   ; margin around plot
 s=2*m+a+b ; length of side of image
 r=(a+b)/2 ; offset (in each of x,y) from centre of 
           ;     image to corner of triangle
 c=m+(a+b)/2 ; position (in each of x,y) of centre of image
 set_plot,'z'
 device,set_res=[s,s]
 tek_color
 erase,1 ; white bg
 c1=15. ; distance to offset characters to centre
 c2=5.  ; extra y-offset for characters
 d=[[0,0,a,0],[0,b,0,0]]  ; vectors to triangle vertices
 d1=[[a,c1,a],[c1,b,b+1.5*c1]]/2  ; vectors to text labels
 lab=['a','b','c']
 cols=[0,2,4,8] ; predefined indices in tek_color
 rot=[[0,-1],[1,0]] ; 90deg rotation matrix
 ori=[[1,0],[0,1]]  ; current rotation matrix
 for i=0,3 do begin ; loop over triangles
     pos=[c,c]+ori##[-r,-r]  ; corner of triangle (use as plot offset)
     draw=ori##d     ; relative vectors allowing for rotation
     label=ori##d1   ; (likewise)
     plots,pos[0]+draw[*,0],pos[1]+draw[*,1],/device,col=cols[i]
     xyouts,pos[0]+label[*,0],pos[1]+label[*,1]-c2,/device,col=cols[i],lab, $
       align=0.5,charsize=1.2   
     ori=rot##ori
 endfor
 image=tvrd()
 tvlct,rr,gg,bb,/get
 write_png,'pythagoras.png',image,rr,gg,bb
 end

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