Databases
StackOverflow2013
Postsdbo
POScaling factor for convolution in matlab to get proper area
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POScaling factor for convolution in matlab to get proper area
    primarykey
    data
    text
    <p>The question is pretty basic, I try to repeat results for continues convolution of two boxcar functions with <code>conv</code> function in matlab. Accordingly to <a href="http://en.wikipedia.org/wiki/Convolution" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Convolution</a> it should result in the area overlap between the two given function. The results of discrete <code>conv</code> should be scaled to get a proper value for the area. Some suggest scaling with sampling frequency, but it does not give correct results for the area. It was suggested to use <code>sum(f)</code> in <a href="https://stackoverflow.com/questions/17412097/scale-factor-in-matlabs-conv">Scale Factor in Matlabs `conv()`</a> but it does not work either. Can anybody explain what scaling factor should be used? Or maybe there is an error in the following code?</p> <pre><code>dx = 0.01 xmin = -0.7; xmax = 0.7; box = @(x) 0.5 * (sign(x - xmin) - sign(x - xmax)); x = -2:dx:2; f1 = box(x); f2 = box(x) * 1.5; conv1 = conv(f1, f2, 'same'); % no scaling conv2 = conv(f1, f2, 'same') * dx; % scale with sampling frequency conv3 = conv(f1 / sum(f1), f2, 'same'); % scale with sum of f1 conv4 = conv(f1, f2 / sum(f2), 'same'); % scale with sum of f2 conv5 = conv(f1 / sum(f1), f2 / sum(f1), 'same'); % scale with sum of f1 and f2 exact = ones(size(x)) * (xmax - xmin) * min(max(f1), max(f2)); plot(x, f1, 'c--o', x, f2, 'm--o' ... % plot functions for reference , x, conv2, 'r-' ... , x, conv3, 'g-' ... , x, conv4, 'b-' ... , x, conv5, 'y-' ... , x, exact, 'k:' ... % excat area ); legend({'f1' 'f2' 'dx scale' 'f1 scale' 'f2 scale' 'f1 and f2 scale' 'exact'}) </code></pre> <p><img src="https://i.stack.imgur.com/pB2c8.png" alt="Results produced by the code above"></p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USzeliboba
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. POScaling factor for convolution in matlab to get proper area
      1. This table or related slice is empty.
      1. VTUpMod
    1. COAs far as my understanding of convolutions go, the red curve looks spot-on. Look at the definition in the Wikipedia article you linked to and substitute 't' with 0. You get a value of 2.1 which is approimately where the figure says the red curve lies
      singulars
      1. POScaling factor for convolution in matlab to get proper area
      1. USbas
    2. COIf you need overlap, something like this would work too: g=[f1;f2]; gmin = min(g,[],1); overlap = trapz(x,gmin); (I assume all functions are positive. If they aren't you need to figure out some algebra.)
      singulars
      1. POScaling factor for convolution in matlab to get proper area
      1. USbas
    3. CO@bas, at t = 0 the position of "boxes" is actually shown in the attache figure, and overlapping area is the area of the small box, that is 1.4. I'd like to understand how `conv` function works, not only find the overlap, but thanks for the hint anyway.
      singulars
      1. POScaling factor for convolution in matlab to get proper area
      1. USzeliboba
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload