A method I used in the past for a similar problem was:
- take the absolute value
- then get the index of the minimum value:
$indexno = $piddle->index(minimum_ind(abs($piddle))
There may be precision problems for very small piddles. You need a
series of values that crosses zero only once.
Good luck
Hernán
Den 2022-10-06 kl. 04:53, skrev Luis Mochan:
Maybe rle can gelp get all sign changes, as in your second example:
pdl> $a=pdl[ 5.3332316, 4.3332316, 3.3332316, 2.3332316, 1.3332316,
0.33323163, -0.66676837, -1.6667684, -2.6667684, -3.6667684]
pdl> p $a
[ 5.3332316 4.3332316 3.3332316 2.3332316 1.3332316 0.33323163
-0.66676837 -1.6667684 -2.6667684 -3.6667684]
pdl> p $a<=>0
[1 1 1 1 1 1 -1 -1 -1 -1]
$a<=>0 is just the sign of the elements of $a
pdl> p +($a<=>0)->rle
[6 4] [1 -1]
which means there are 6 1's followed by 4 -1's
pdl> ($rle)=($a<=>0)->rle;
$rle has [6 4]
pdl> p $rle((0))-1
5
I choose the first sign change with ((0)) and subtract 1 to get the
index from the number of elements.
You can put everything together as in
pdl> p +[($a<=>0)->rle]->[0]->((0))-1
5
You could generalize this to get further resonances in more
complicated circuits.
Regards,
Luis
On Wed, Oct 05, 2022 at 06:50:32PM -0700, Eric Wheeler wrote:
Hello all,
I'm trying to find the series resonant frequency of an RF component, which
is where the component reactance switches from positive to negtive or
vice-versa.
Given an N-vector PDL of sorted elements, I need to know at what index it
switches from positive to negative.
Here are some examples; in real life these are real values from physical
measurements, so they are never going to be nice round integers---but you
can assume they will be sorted in ascending or descending order.
Example 1:
pdl> p sequence(10)-5
[-5 -4 -3 -2 -1 0 1 2 3 4]
^^
I need to know "index 4" is the place at which it switches.
Example 2:
pdl> p ((-sequence(10))+5+rand())
[ 5.3332316 4.3332316 3.3332316 2.3332316 1.3332316 0.33323163
-0.66676837 -1.6667684 -2.6667684 -3.6667684]
^^^^^^^^^^
In this floating-point example it would be "index 5"
Is there already a "PDL-broadcast-way" of doing this?
How would you do it?
--
Eric Wheeler
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