[metapost] Drawing a urn

Martin Kaffanke technik at roomandspace.com
Thu Nov 29 13:09:53 CET 2007

```Hi there!

I'd like to draw an urn where we have a probability of .57 to get a dark
ball when we choose a random ball.

I have the following:

u := 5mm;
s := .05u;

draw (0,10u+s)--(0,.5u)..(.15u,.15u)..(.5u,0)
--(9.5u+2s,0)..(9.85u+2s,.15u)..(10u+2s,.5u)--(10u+2s , 10u+s);

path c;
for i=1 upto 10:
for j=1 upto 10:
c := fullcircle scaled 1u shifted (j*u-u/2+s,i*u-u/2+s);
if (i <= 5 ):
fill c withcolor .7white;
else:
fill c withcolor .4white;
fi;
endfor;
endfor;

This looks nice, but it shows a fifty-fifty chance.  How would you go
further to show a chance of .57 instead of .5?

Second: !important! I'd like to have the balls randomized.  In a java
application I do the same by creating 100 boolean values (true = dark,
false = white) something like

for i=1 upto 100:
if i <= .57:
values.append(.4white);
else:
values.append(.7white);
fi;
endfor;

mix(values);

How could that be done correctly with metapost?

Thanks,
Martin

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