plot_lc.m

这是在网上下的一个东东

function plot_lc(rho,eta,marker,ps,reg_param) 
%PLOT_LC Plot the L-curve. 
% 
% plot_lc(rho,eta,marker,ps,reg_param) 
% 
% Plots the L-shaped curve of the solution norm 
%    eta = || x ||      if   ps = 1 
%    eta = || L x ||    if   ps = 2 
% as a function of the residual norm rho = || A x - b ||.  If ps is 
% not specified, the value ps = 1 is assumed. 
% 
% The text string marker is used as marker.  If marker is not 
% specified, the marker '-' is used. 
% 
% If a fifth argument reg_param is present, holding the regularization 
% parameters corresponding to rho and eta, then some points on the 
% L-curve are identified by their corresponding parameter. 
 
% Per Christian Hansen, IMM, 12/29/97. 
 
% Set defaults. 
if (nargin==2), marker = '-'; end  % Default marker. 
if (nargin < 4), ps = 1; end       % Std. form is default. 
np = 10;                           % Number of identified points. 
 
% Initialization. 
if (ps < 1 | ps > 2), error('Illegal value of ps'), end 
n = length(rho); ni = round(n/np); 
 
% Make plot. 
loglog(rho(2:end-1),eta(2:end-1)), ax = axis; 
if (max(eta)/min(eta) > 10 | max(rho)/min(rho) > 10) 
  if (nargin < 5) 
    loglog(rho,eta,marker), axis(ax) 
  else 
    loglog(rho,eta,marker,rho(ni:ni:n),eta(ni:ni:n),'x'), axis(ax) 
    HoldState = ishold; hold on; 
    for k = ni:ni:n 
      text(rho(k),eta(k),num2str(reg_param(k))); 
    end 
    if (~HoldState), hold off; end 
  end 
else 
  if (nargin < 5) 
    plot(rho,eta,marker), axis(ax) 
  else 
    plot(rho,eta,marker,rho(ni:ni:n),eta(ni:ni:n),'x'), axis(ax) 
    HoldState = ishold; hold on; 
    for k = ni:ni:n 
      text(rho(k),eta(k),num2str(reg_param(k))); 
    end 
    if (~HoldState), hold off; end 
  end 
end 
xlabel('residual norm || A x - b ||_2') 
if (ps==1) 
  ylabel('solution norm || x ||_2') 
else 
  ylabel('solution semi-norm || L x ||_2') 
end 
title('L-curve')