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Why can't I find exponential of a "complex256" matrix?

asked 2013-11-09 10:47:13 -0500

Shashank gravatar image

updated 2015-01-17 15:30:12 -0500

FrédéricC gravatar image

The following script gives me a error - ValueError: invalid type: complex256. However, this works with complex128. Is there a way to make expm work with complex256?

import scipy
a=scipy.matrix([[1,0],[0,1]],dtype='complex256')
scipy.linalg.expm(a)
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answered 2013-11-09 14:10:40 -0500

kcrisman gravatar image

This is really not a Sage question...

Nonetheless, a quick glance at the source reveals that it just isn't implemented.

if A.dtype == 'float64' or A.dtype == 'complex128':
    if A_L1 < 1.495585217958292e-002:
        U,V = _pade3(A, ident)
    elif A_L1 < 2.539398330063230e-001:
        U,V = _pade5(A, ident)
    elif A_L1 < 9.504178996162932e-001:
        U,V = _pade7(A, ident)
    elif A_L1 < 2.097847961257068e+000:
        U,V = _pade9(A, ident)
    else:
        maxnorm = 5.371920351148152
        n_squarings = max(0, int(ceil(log2(A_L1 / maxnorm))))
        A = A / 2**n_squarings
        U,V = _pade13(A, ident)
elif A.dtype == 'float32' or A.dtype == 'complex64':
    if A_L1 < 4.258730016922831e-001:
        U,V = _pade3(A, ident)
    elif A_L1 < 1.880152677804762e+000:
        U,V = _pade5(A, ident)
    else:
        maxnorm = 3.925724783138660
        n_squarings = max(0, int(ceil(log2(A_L1 / maxnorm))))
        A = A / 2**n_squarings
        U,V = _pade7(A, ident)
else:
    raise ValueError("invalid type: "+str(A.dtype))
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Comments

I've opened https://github.com/scipy/scipy/issues/3051 as an enhancement request for this.

kcrisman gravatar imagekcrisman ( 2013-11-09 14:15:43 -0500 )edit

Thanks a lot!

Shashank gravatar imageShashank ( 2013-11-09 16:12:38 -0500 )edit

Scipy has passed it on to Numpy... https://github.com/numpy/numpy/issues/4035

kcrisman gravatar imagekcrisman ( 2013-11-11 01:51:17 -0500 )edit

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Asked: 2013-11-09 10:47:13 -0500

Seen: 169 times

Last updated: Nov 09 '13