# matchms.similarity.CosineGreedy module¶

class matchms.similarity.CosineGreedy.CosineGreedy(tolerance: float = 0.1, mz_power: float = 0.0, intensity_power: float = 1.0)[source]

Calculate ‘cosine similarity score’ between two spectra.

The cosine score aims at quantifying the similarity between two mass spectra. The score is calculated by finding best possible matches between peaks of two spectra. Two peaks are considered a potential match if their m/z ratios lie within the given ‘tolerance’. The underlying peak assignment problem is here solved in a ‘greedy’ way. This can perform notably faster, but does occasionally deviate slightly from a fully correct solution (as with the Hungarian algorithm, see `CosineHungarian`). In practice this will rarely affect similarity scores notably, in particular for smaller tolerances.

For example

```import numpy as np
from matchms import Spectrum
from matchms.similarity import CosineGreedy

reference = Spectrum(mz=np.array([100, 150, 200.]),
intensities=np.array([0.7, 0.2, 0.1]))
query = Spectrum(mz=np.array([100, 140, 190.]),
intensities=np.array([0.4, 0.2, 0.1]))

# Use factory to construct a similarity function
cosine_greedy = CosineGreedy(tolerance=0.2)

score = cosine_greedy.pair(reference, query)

print(f"Cosine score is {score['score']:.2f} with {score['matches']} matched peaks")
```

Should output

```Cosine score is 0.83 with 1 matched peaks
```
__init__(tolerance: float = 0.1, mz_power: float = 0.0, intensity_power: float = 1.0)[source]
Parameters
• tolerance – Peaks will be considered a match when <= tolerance apart. Default is 0.1.

• mz_power – The power to raise m/z to in the cosine function. The default is 0, in which case the peak intensity products will not depend on the m/z ratios.

• intensity_power – The power to raise intensity to in the cosine function. The default is 1.

matrix(references: , queries: , is_symmetric: bool = False)

Optional: Provide optimized method to calculate an numpy.array of similarity scores for given reference and query spectrums. If no method is added here, the following naive implementation (i.e. a double for-loop) is used.

Parameters
• references – List of reference objects

• queries – List of query objects

• is_symmetric – Set to True when references and queries are identical (as for instance for an all-vs-all comparison). By using the fact that score[i,j] = score[j,i] the calculation will be about 2x faster.

pair(reference: Spectrum, query: Spectrum) [source]

Calculate cosine score between two spectra.

Parameters
• reference – Single reference spectrum.

• query – Single query spectrum.

Returns

Tuple with cosine score and number of matched peaks.

Return type

Score

sort(scores: numpy.ndarray)

Return array of indexes for sorted list of scores. This method can be adapted for different styles of scores.

Parameters

scores – 1D Array of scores.

Returns

Indexes of sorted scores.

Return type

idx_sorted