[SciPy-User] bug in signal.lsim2

Ryan Krauss ryanlists@gmail....
Thu Jan 28 17:00:19 CST 2010


Hmmm.  Thanks.  That solves the immediate problem.  I am letting my
students choose between Matlab and Python for projects in my course.
This one my erode their confidence in Python/Scipy a bit.

On Thu, Jan 28, 2010 at 3:05 PM,  <josef.pktd@gmail.com> wrote:
> On Thu, Jan 28, 2010 at 3:39 PM, Ryan Krauss <ryanlists@gmail.com> wrote:
>> I believe I have discovered a bug in signal.lsim2.  I believe the
>> short attached script illustrates the problem.  I was trying to
>> predict the response of a transfer function with a pure integrator:
>>
>>              g
>> G = -------------
>>          s(s+p)
>>
>> to a finite width pulse.  lsim2 seems to handle the step response just
>> fine, but says that the pulse response is exactly 0.0 for the entire
>> time of the simulation.  Obviously, this isn't the right answer.
>>
>> I am running scipy 0.7.0 and numpy 1.2.1 on Ubuntu 9.04, but I also
>> have the same problem on Windows running 0.7.1 and 1.4.0.
>>
>> Thanks,
>>
>> Ryan
>
> When I add a small noise
>
> u2 = zeros(N) + 1e-14
>
> or for
> u2[:50] = amp
>
> or for
> u2[50:200] = amp
>
> it seems to work.
>
> This might be a tricky bug.
>
> Josef
>
>
>>
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>>
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