% BODE
% This program takes four parameters in what could be
% either an amplitude or a phase Bode plot:
%   y1: decibels (or degrees) at the known end of the
%       inclined segment (could be the left or right end).
%   w1: angular frequency (rad/s) at y1.
%   w2: angular frequency (rad/s) at the far end from y1.
%   slope: slope of the segment going from w1 to w2, that
%       means that the slope would go from right to left
%       if the end point of the segment that we know is
%       the right end.
% Output:
%   It echos w1 w2 y1 the slope and gives new:
%   y2: the vertical value (dB or deg) at w2.
%   dy: vertical drop (or climb) in dB or deg.
%   dec: distance from w1 to w2 in decades.
%
% By L.Linares 2011
%
%          y1--+
%              |\
%              | \  (negative slope from w1 to w2)
%                 \
%             w1   \
%                   +---y2
%                   |
%                   w2
%
%          y2--+
%              |\
%              | \  (positive slope from w1 to w2)
%                 \
%             w2   \
%                   +---y1
%                   |
%                   w1


% VERY IMPORTANT: To type this program on a regular
%   text file, I had to replace some HP50 keys by
%   certain strings. So ...
%   Where I wrote        you type
%        *               [multiply key]
%        ACOS            [WHITE SHIFT] COS
%        ^               [y to the x key]
%        SQRT            press square root key (*)
%        ->TAG           [WHITE SHIFT] PRG/TYPE/->TAG
%        ->              [RED SHIFT] [zero key]
%   (*) Do NOT type the letters SQRT ... it won't work!

% I "travel" along the plot, from the first "knee" to the 
% second, then check the echoed data, delete all but the
% new y2 just computed, and enter the new w1 w2 slope, etc.

% Modification on April 15, 2011:
% The two system flags -3 and -105 are set to ensure
% numerical results, but are set back to their original
% values, so the user sees the same functionability that
% he/she was using before issuing a call to BODE.

% This program is provided on a "as is" basis, for
% reference ONLY, and no warranty of its accuracy or
% correctness is made. If you use it, you use it at your
% own risk.

<< 
  "Y1 W1 W2 SLOPE" PROMPT
  -3 FS? -105 FS?
  -> Y1 W1 W2 SLP F3 F105
  <<
    'LOG(W2/W1)' EVAL DUP SLP *  
    -> DX DY
    <<
      Y1 'Y1' ->TAG
      Y1 DY + 'Y2' ->TAG
      W1 'W1' ->TAG
      W2 'W2' ->TAG
      SPL 'slope' ->TAG
      DX 'dec' ->TAG
      DY 'Dy' ->TAG
      IF 'F3==0' THEN -3 SF END
      IF 'F105==0' THEN -105 SF END
    >> 
  >> 
>>