\\ v is a vector of pairs = [[x1,y1],[x2,y2],...].
t_writedots (file,v,format="(%.2f,%.2f)",rowlen=10) = {my (n,w);
n=#v; w=vector(n,i,Strprintf(format,v[i][1],v[i][2]));
T=t_table(w,rowlen); t_write(file,T)}

\\ Writes pairs of args and vals to a file,
\\ e.g. for plotting with pst-plot. If args is
\\ a number, args start  with this number;
\\ otherwise args has to be a vector.
t_writeplotpairs (file,vals,args=0,rowlen=20,format="%.4f") = {my (n,w,T);
n=#vals; vals=[Strprintf(format,x) | x<-vals];
if (type(args)=="t_VEC",args=[Strprintf(format,x) | x<-args];
w=vector(2*n,i, if (i%2, args[i\2+1], vals[i\2])),
w=vector(2*n,i, if(i%2, i\2+args, vals[i\2])));
T=t_table(w,rowlen); t_write(file,T)}

t_writewalk (file=0,v,neg=1,m=200,format="%.2f") = {my (n,w,s);
m=min(m,#v); v=v[1..m]; n=#v;
if (neg, v=apply(x->if(x==0,-1,x),v));
w=vector(n,i,0); s=0; for (i=1,n,s+=v[i]; w[i]=s);
if (file, t_writeplotpairs(file,w,,,format), t_out(w,format))}