MetaFun - Pragma ADE

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\startMPdefinitions{solvers}
angle_radius := 10pt ;
def mark_rt_angle (expr a, b, c) =
draw ((1,0)--(1,1)--(0,1))
zscaled (angle_radius*unitvector(a-b))
shifted b
enddef ;
\stopMPdefinitions
So far, most equations are rather simple, and in order to solve them, METAPOST did not have to work
real hard. The only boundary condition is that in order to find a solution, METAPOST must be able
to solve all dependencies.
The actual value of the whatever variable is that it saves us from introducing a slew of variables
that will never be used again. We could write:
z0 = A[z1,z3] = B[z2,z4] ;
and get the same result, but the whatever variable saves us the trouble of introducing intermediate
variables for which we have no use once the calculation is finished.
The macro mark_rt_angle draws the angle symbol and later we will see how it is defined. First
we draw the labels. Unfortunately we cannot package btex ... etex into a macro, because it is
processed in a rather special way. Each btex ... etex occurance is filtered from the source and
converted into a snippet of TEX code. When passed through TEX, each snippet becomes a page, and
an auxiliary program converts each page into a METAPOST picture definition, which is loaded by
METAPOST. The limitation lays in the fact that the filtering is done independent from the METAPOST
run, which means that loops (and other code) are not seen at all. Later we will introduce the
METAFUN way around this.
In order to get all the labels typeset, we have to put a lot of code here. The macro dotlabel draws
a dot and places the typeset label.
\startMPdefinitions{solvers}
def draw_problem_labels =
pickup pencircle scaled 5pt ;
dotlabel.llft("$Z_{11}$", z11) ; dotlabel.ulft("$Z_{12}$", z12) ;
dotlabel.ulft("$Z_{13}$", z13) ; dotlabel.llft("$Z_{14}$", z14) ;
dotlabel.lrt ("$Z_{21}$", z21) ; dotlabel.llft("$Z_{22}$", z22) ;
dotlabel.urt ("$Z_{23}$", z23) ; dotlabel.ulft("$Z_{24}$", z24) ;
dotlabel.urt ("$Z_{31}$", z31) ; dotlabel.ulft("$Z_{32}$", z32) ;
dotlabel.urt ("$Z_{33}$", z33) ; dotlabel.urt ("$Z_{34}$", z34) ;
dotlabel.lrt ("$Z_{41}$", z41) ; dotlabel.urt ("$Z_{42}$", z42) ;
dotlabel.llft("$Z_{43}$", z43) ; dotlabel.lrt ("$Z_{44}$", z44) ;
dotlabel.urt ("$Z_{0}$", z0) ;
dotlabel.lft ("$Z_{1}$", z1) ; dotlabel.top ("$Z_{2}$", z2) ;
Welcome to MetaPost Linear equations