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Colleagues I'm having problems with an Arithmetic Overflow error when calculating the x and y values for functions of the form: y = ax^4 + bx^3 + cx^2 + dx + e to which I then add a bit of randomness and other embellishments. I have had a look in the Metafun and Metafont manuals but nothing jumps out at me. In the minimum working example below, this Arithmetic Overflow occurs when xord =13.5 but I can get the calculation to work if I separate out the equation and then add together, since it seems to be failing on the pow(xord,4) instruction. Is there a switch in MetaFont that should be set or a better way of getting round this Arithmetic Overflow error? Thanks Best Wishes Keith McKay %%%%%%%%%%%%%MWE%%%%%%%%%%% \setuppapersize [A4,landscape] \starttext \startMPpage StartPage; width := PaperWidth ; height := PaperHeight ; unit := cm ; path p; p := unitsquare scaled .1cm ; path pat; pat := (0.0*cm,19.935*cm); for xord = 0 step 0.1 until 25: show xord; %%%%%%%%fails at xord = 13.5%%%%%%%%% yord := ((-0.000268117) * pow(xord,4)) +(0.0136949 * pow(xord, 3)) + ((-0.16608) * sqr(xord)) + ((-0.771743) * xord) + 19.935; %%%%%comment out above and uncomment below and it works%%%% % yord1 := (-0.000268117) * sqr(xord); % yord1a := yord1 * sqr(xord); % yord2 := (0.0136949 * pow(xord, 3)); % yord3 := ((-0.16608) * sqr(xord)); % yord4 := ((-0.771743) * xord); % yord := yord1 + yord1a + yord2 + yord3 + yord4 + 19.935; xrand := (uniformdeviate(1) - 0.5)*2; yrand := uniformdeviate(1) - 0.5; xcoord := xord + xrand; ycoord := yord + yrand; if odd xord: pat := pat ... (xcoord*cm, ycoord*cm); else: pat := pat --- (xcoord*cm, ycoord*cm); fill p shifted (xcoord*cm, ycoord*cm) withcolor (uniformdeviate(1),uniformdeviate(1),uniformdeviate(1)) ; fi; draw pat withpen pencircle scaled (uniformdeviate(0.75)*mm) withcolor (uniformdeviate(1),uniformdeviate(1),uniformdeviate(1)); %withtransparency (1, .5); drawdot (xcoord*cm, ycoord*cm) withpen pencircle scaled (uniformdeviate(2.5)*mm) withcolor (uniformdeviate(1),uniformdeviate(1),uniformdeviate(1)); endfor; StopPage; \stopMPpage \stoptext