Let's try this. It's BUGGERED.

src/cmd/eqn/matrix.c

@@ -0,0 +1,78 @@
+#include "e.h"
+
+startcol(int type)	/* mark start of column in lp[] array */
+{
+	int oct = ct;
+
+	lp[ct++] = type;
+	lp[ct++] = 0;	/* count, to come */
+	lp[ct++] = 0;	/* separation, to come */
+	return oct;
+}
+
+void column(int oct, int sep)	/* remember end of column that started at lp[oct] */
+{
+	int i, type;
+
+	lp[oct+1] = ct - oct - 3;
+	lp[oct+2] = sep;
+	type = lp[oct];
+	if (dbg) {
+		printf(".\t%d column of", type);
+		for (i = oct+3; i < ct; i++ )
+			printf(" S%d", lp[i]);
+		printf(", rows=%d, sep=%d\n", lp[oct+1], lp[oct+2]);
+	}
+}
+
+void matrix(int oct)	/* matrix is list of columns */
+{
+	int nrow, ncol, i, j, k, val[100];
+	double b, hb;
+	char *space;
+	extern char *Matspace;
+
+	space = Matspace;	/* between columns of matrix */
+	nrow = lp[oct+1];	/* disaster if rows inconsistent */
+				/* also assumes just columns */
+				/* fix when add other things */
+	ncol = 0;
+	for (i = oct+1; i < ct; i += lp[i]+3 ) {
+		ncol++;
+		dprintf(".\tcolct=%d\n", lp[i]);
+	}
+	for (k=1; k <= nrow; k++) {
+		hb = b = 0;
+		j = oct + k + 2;
+		for (i=0; i < ncol; i++) {
+			hb = max(hb, eht[lp[j]]-ebase[lp[j]]);
+			b = max(b, ebase[lp[j]]);
+			j += nrow + 3;
+		}
+		dprintf(".\trow %d: b=%g, hb=%g\n", k, b, hb);
+		j = oct + k + 2;
+		for (i=0; i<ncol; i++) {
+			ebase[lp[j]] = b;
+			eht[lp[j]] = b + hb;
+			j += nrow + 3;
+		}
+	}
+	j = oct;
+	for (i=0; i<ncol; i++) {
+		pile(j);
+		val[i] = yyval;
+		j += nrow + 3;
+	}
+	yyval = salloc();
+	eht[yyval] = eht[val[0]];
+	ebase[yyval] = ebase[val[0]];
+	lfont[yyval] = rfont[yyval] = 0;
+	dprintf(".\tmatrix S%d: r=%d, c=%d, h=%g, b=%g\n",
+		yyval,nrow,ncol,eht[yyval],ebase[yyval]);
+	printf(".ds %d \"", yyval);
+	for( i=0; i<ncol; i++ )  {
+		printf("\\*(%d%s", val[i], i==ncol-1 ? "" : space);
+		sfree(val[i]);
+	}
+	printf("\n");
+}