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Look at bug reports 6744 and 6745 at <a class="moz-txt-link-freetext" href="http://bugzilla.scilab.org">http://bugzilla.scilab.org</a><br>
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6744 has an attachment with my own functions. Probably not perfect as
well !<br>
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Vladímir Rodríguez a écrit :
<blockquote cite="mid:1268152835.3338.1.camel@accionamiento" type="cite">
<pre wrap="">El mar, 09-03-2010 a las 16:39 +0100, David PICARD escribió:
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<pre wrap="">Well, I eventually came up to the conclusion that both p_margin() and
g_margin() are buggy. I had to write my own code to replace them.
I can give details upon request.
Regards.
David PICARD a écrit :
</pre>
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<pre wrap="">I corrected the subject.
David PICARD a écrit :
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<pre wrap="">I get weird results when I try to calculate gain margin for transfer
functions. For example, this one :
-->Hbo=syslin(1.0,(0.263-0.656*z+0.206*z^2+0.3*z^3)/(-0.263+0.656*z+0.28*z^2-1.674*z^3+z^4))
Hbo_s =
2 3 0.263 - 0.656z + 0.206z
+ 0.3z ----------------------------------
2 3 4 - 0.263 + 0.656z + 0.28z -
1.674z + z It is a digital controller open loop transfer function.
Phase margin : p_margin(Hbo_s) returns 65.62, which is correct
(checked with both a book and Matlab).
Gain margin : g_margin(Hbo_s) returns -41.06, which I is not what I
expect.
So, I plot the frequency response with :
-->show_margins(Hbo_s,'nyquist')
to try to figure out the gain margin graphically.
The gain margin is the inverse of the gain of the transfer function
when the phase is -180°).
The curve crosses the X axis at -0.368, which leads to gain_margin =
1/0.368 = 2.7, which is the value given in my book and returned by
Matlab (margin() ).
In addition, the blue line that I assume, shows the gain margin,
extends way beyond -0.368, probably as far as -41.06.
Did I get something wrong here ? Thanks.
My configuration : Scilab 5.2.1, Windows XP SP3
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</pre>
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<pre wrap=""><!---->I am interested in every detail about it, I am going to use these
function in clases.
Thanks
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