scipy.signal.choose_conv_method¶

scipy.signal.
choose_conv_method
(in1, in2, mode='full', measure=False)[source]¶ Find the fastest convolution/correlation method.
This primarily exists to be called during the
method='auto'
option inconvolve
andcorrelate
, but can also be used when performing many convolutions of the same input shapes and dtypes, determining which method to use for all of them, either to avoid the overhead of the ‘auto’ option or to use accurate realworld measurements.Parameters:  in1 : array_like
The first argument passed into the convolution function.
 in2 : array_like
The second argument passed into the convolution function.
 mode : str {‘full’, ‘valid’, ‘same’}, optional
A string indicating the size of the output:
full
The output is the full discrete linear convolution of the inputs. (Default)
valid
The output consists only of those elements that do not rely on the zeropadding.
same
The output is the same size as in1, centered with respect to the ‘full’ output.
 measure : bool, optional
If True, run and time the convolution of in1 and in2 with both methods and return the fastest. If False (default), predict the fastest method using precomputed values.
Returns:  method : str
A string indicating which convolution method is fastest, either ‘direct’ or ‘fft’
 times : dict, optional
A dictionary containing the times (in seconds) needed for each method. This value is only returned if
measure=True
.
Notes
For large n,
measure=False
is accurate and can quickly determine the fastest method to perform the convolution. However, this is not as accurate for small n (when any dimension in the input or output is small).In practice, we found that this function estimates the faster method up to a multiplicative factor of 5 (i.e., the estimated method is at most 5 times slower than the fastest method). The estimation values were tuned on an early 2015 MacBook Pro with 8GB RAM but we found that the prediction held fairly accurately across different machines.
If
measure=True
, time the convolutions. Because this function usesfftconvolve
, an error will be thrown if it does not support the inputs. There are cases whenfftconvolve
supports the inputs but this function returns direct (e.g., to protect against floating point integer precision).New in version 0.19.
Examples
Estimate the fastest method for a given input:
>>> from scipy import signal >>> a = np.random.randn(1000) >>> b = np.random.randn(1000000) >>> method = signal.choose_conv_method(a, b, mode='same') >>> method 'fft'
This can then be applied to other arrays of the same dtype and shape:
>>> c = np.random.randn(1000) >>> d = np.random.randn(1000000) >>> # `method` works with correlate and convolve >>> corr1 = signal.correlate(a, b, mode='same', method=method) >>> corr2 = signal.correlate(c, d, mode='same', method=method) >>> conv1 = signal.convolve(a, b, mode='same', method=method) >>> conv2 = signal.convolve(c, d, mode='same', method=method)