Newbie problems with plot2d



Neither of the two approaches used in the following script generates 
arguments acceptable to plot2d.  (My intent is to use maxima for 
prototyping and debugging fortran, so I want to stay as close as 
possible to fortran idiom, particularly with respect to array usage.) 
Any help would be appreciated.

**********************
lognormal(x) := (1/x)*exp(-(log(x/x0))^2/(2*sig^2));
tfmi(t) := first(quad_qagi(lognormal(s)*exp(-s*t), s, 10^-16, inf));
x0:2; sig:2; amp:0.1;
tfmi(0.1); /* OK */
tfmi(1.0); /* OK */
numberp(tfmi(0.1)); /* true */
plot2d(tfmi(t),[t,0.1,1]); /* fails */

array(tvec, 20);
array(yvec, 20);
for i:0 step 1 thru 19 do
block(
   tvec[i]: 0.1*i,
   yvec[i]: tfmi(tvec[i])
   );
display(tvec[3],yvec[3]); /* OK */
plot2d([discrete,tvec,yvec]);  /* fails */