function [B,A,n] = iirafilt(type,fp,fs,Ap,As)

% [B,A] = function iirdfilt(type,fp,fs,Ap,As)
%
% type es el tipo de filtro, 'butter', 'cheby1', 'cheby2'
% fp es la/las frecuencia/s de pasabanda en Hz
% fs es la/las frecuencia/s de parabanda en Hz
% Ap y As son las atenuaciones respectivas en decibelios
 

if length(fp) ~= length(fs)
   disp('Error en dimensiones de fp y/o fs');
   return
end

if Ap > As,
   disp('Error en los valores de Ap y/o As');
   return;
end

% Determinar el tipo de filtro: pasabajo, pasoalto, paabanda o parabanda
if (length(fp) == 1)
   if (fp < fs),
      tipo = 'lp';
   elseif (fp > fs)
      tipo = 'hp';
   else
      disp('Frecuencia de pasabanda = Frecuencia de parabanda');
      return;
   end
elseif (length(fp) == 2)
   aux = [fp fs];
   [aux1,i]=sort(aux);
   if (i==[3 1 2 4])
      tipo = 'bp';
   elseif (i==[1 3 4 2])
      tipo = 'bs';
   else
      disp('Error: Compruebe que los valores de fp y fs están en el orden correcto');
      return;
   end
end

wp = 2*pi*fp;
ws = 2*pi*fs;

switch tipo
case 'lp',
   switch type
   case 'butter',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = log10(sqrt(aux/e2))/log10(ws/wp); n = ceil(n);
      wc = (1/e2)^(1/(2*n));
      [Z,P,K]=buttap(n);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2lp(Ban,Aan,wc*wp);
   case 'cheby1',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = acosh(sqrt(aux/e2))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb1ap(n,Ap);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2lp(Ban,Aan,wp);   
   case 'cheby2',
      e2 = 1/(10^(0.1*As)-1);
      aux = 10^(0.1*Ap)-1;
      n = acosh(sqrt(1/(aux*e2)))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb2ap(n,As);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2lp(Ban,Aan,ws);
   end
case 'hp',
   wp = 1/wp;
   ws = 1/ws;
   switch type
   case 'butter',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = log10(sqrt(aux/e2))/log10(ws/wp); n = ceil(n);
      wc = (1/e2)^(1/(2*n));      
      [Z,P,K]=buttap(n);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2hp(Ban,Aan,1/(wc*wp));
   case 'cheby1',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = acosh(sqrt(aux/e2))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb1ap(n,Ap);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2hp(Ban,Aan,1/wp);   
   case 'cheby2',
      e2 = 1/(10^(0.1*As)-1);
      aux = 10^(0.1*Ap)-1;
      n = acosh(sqrt(1/(aux*e2)))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb2ap(n,As);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2hp(Ban,Aan,1/ws);
   end
case 'bp'   % Hay que pasar a pasobajo las especificaciones
   wx2 = wp(1)*wp(2);wx = sqrt(wx2);
   if (ws(1)*ws(2) < wx2),
      ws(1) = wx2/ws(2);
   else
      ws(2) = wx2/ws(1);
   end
   wp = wp(2)-wp(1);
   ws = ws(2)-ws(1);
   
   switch type
   case 'butter',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = log10(sqrt(aux/e2))/log10(ws/wp); n = ceil(n);
      wc = (1/e2)^(1/(2*n));
      [Z,P,K]=buttap(n);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2bp(Ban,Aan,wx,wp*wc);
    case 'cheby1',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = acosh(sqrt(aux/e2))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb1ap(n,Ap);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2bp(Ban,Aan,wx,wp);   
   case 'cheby2',
      e2 = 1/(10^(0.1*As)-1);
      aux = 10^(0.1*Ap)-1;
      n = acosh(sqrt(1/(aux*e2)))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb2ap(n,As);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2bp(Ban,Aan,wx,ws);
   end
   
case 'bs',
   wx2 = ws(1)*ws(2);wx = sqrt(wx2);
   if (wp(1)*wp(2) < wx2),
      wp(1) = wx2/wp(2);
   else
      wp(2) = wx2/wp(1);
   end
   wp = 1/(wp(2)-wp(1));
   ws = 1/(ws(2)-ws(1));
   
   switch type
   case 'butter',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = log10(sqrt(aux/e2))/log10(ws/wp); n = ceil(n);
      wc = (1/e2)^(1/(2*n));
      [Z,P,K]=buttap(n);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2bs(Ban,Aan,wx,1/(wp*wc));
    case 'cheby1',
      e2 = 10^(0.1*Ap)-1;
      aux = 10^(0.1*As)-1;
      n = acosh(sqrt(aux/e2))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb1ap(n,Ap);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2bs(Ban,Aan,wx,1/wp);   
   case 'cheby2',
      e2 = 1/(10^(0.1*As)-1);
      aux = 10^(0.1*Ap)-1;
      n = acosh(sqrt(1/(aux*e2)))/acosh(ws/wp); n = ceil(n);
      [Z,P,K]=cheb2ap(n,As);
      [Ban,Aan]=zp2tf(Z,P,K);
      [Ban,Aan] = lp2bs(Ban,Aan,wx,1/ws);
   end
end



[H2,W]=freqs(Ban,Aan,500);
H2db = 20*log10(abs(H2));

figure;
if (length(fp) == 1)
   plot(W/(2*pi),H2db,[fp fs],-[Ap As],'*');grid;zoom;
else
   plot(W/(2*pi),H2db,[fp fs],-[Ap Ap As As],'*');grid;zoom;
end

A=Aan;
B=Ban;

return;