tinv.m

这是在网上下的一个东东

%
% t=tinv(p,nu)
%
function t=tinv(p,nu)
%
% Special cases.
%
if (p >= 1.0),
  t=+Inf;
  return;
end;
if (p<=0.0),
  t=-Inf;
  return;
end;
%
% First, figure out whether t>1/2 or t<1/2.
%
if (p<0.5),
  t=-tinv(1-p,nu);
  return;
else
  l=0.0;
  r=1.0;
  while (tcdf(r,nu) < p)
    l=r;
    r=r*2;
  end
%
% Now, we've got a bracket around t.  Use bisection to tighten it up.
%
  while (((r-l)/r) > 1.0e-5)
    m=(l+r)/2;
    if (tcdf(m,nu) > p)
      r=m;
    else
      l=m;
    end
  end
end
t=(l+r)/2;