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i have to save a matrix shown below with complex data into a file with .H extension using savetxt command of numpy but i am not able to save it.the matrix to be saved is

[[ 1.0+0.j 0.0+0.j 0.0+0.j] [ 1.0+0.j 1.0+0.j 0.0+0.j] [ 2.0+0.j 2.0+0.j 0.0+0.j] ..., [ 683.0+0.j 688.0+0.j -2.7+0.j] [ 684.0+0.j 689.0+0.j -2.7+0.j] [ 685.0+0.j 690.0+0.j -2.7+0.j]]

i have tried this command but its giving error 

>>savetxt('H.H',H_new.H,fmt='%.4e%+.4j%.4e%+.4j%.4e%+.4j',delimiter=' '); Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.7/dist-packages/numpy/lib/npyio.py", line 974, in savetxt % fmt) AttributeError: fmt has wrong number of % formats. %.4e%+.4j%.4e%+.4j%.4e%+.4j
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  • What version of numpy are you using? (Check numpy.__version__.) Commented Jan 9, 2014 at 6:09
  • i am using 1.6.1 version of numpy Commented Jan 26, 2014 at 6:39
  • I updated my answer with a method that works in numpy 1.6.1. Commented Jan 26, 2014 at 13:40
  • thanks for ur reply but i updated my numpy to 1.7.1 and ur earliar solution is working fine Commented Jan 27, 2014 at 4:53
  • i have one more query that if i want to import this same complex values containing file in my program what procedure should i follow? Commented Jan 27, 2014 at 5:07

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Your format string is missing some format characters. Try something like

fmt='%.4e%+.4ej %.4e%+.4ej %.4e%+.4ej'

But it looks like you'll need numpy 1.7.0 or later; see https://github.com/numpy/numpy/commit/1475319160baed782daa39e0de0c0655c2abe4b5

It worked for me with numpy 1.8.0, but not with 1.6.1.

With numpy 1.6.1, you can save the data in this format by first creating a real view of the complex data.

In this example (an ipython session), I'm using numpy 1.6.1:

In [28]: np.__version__ Out[28]: '1.6.1'

z is a complex array, with shape (2, 3):

In [29]: z Out[29]: array([[ 1.+2.j, -3.+4.j, 5.-6.j], [-1.+0.j, 0.+2.j, 3.+0.j]])

Use the view method to create a real array with shape (2, 6):

In [30]: rz = z.view(float) In [31]: rz Out[31]: array([[ 1., 2., -3., 4., 5., -6.], [-1., 0., 0., 2., 3., 0.]])

Save the array using savetxt. The format string uses the entire row, so there is no need to give the delimiter argument:

In [32]: savetxt('z.txt', rz, fmt='%.4e%+.4ej %.4e%+.4ej %.4e%+.4ej')

Take a look at the output:

In [33]: !cat z.txt 1.0000e+00+2.0000e+00j -3.0000e+00+4.0000e+00j 5.0000e+00-6.0000e+00j -1.0000e+00+0.0000e+00j 0.0000e+00+2.0000e+00j 3.0000e+00+0.0000e+00j

This file can be read back into a numpy array with np.loadtxt or np.genfromtxt. To use loadtxt, it must be told that the data type is complex:

In [8]: loadtxt('z.txt', dtype=np.complex128) Out[8]: array([[ 1.+2.j, -3.+4.j, 5.-6.j], [-1.+0.j, 0.+2.j, 3.+0.j]])

genfromtxt works with the same arguments. genfromtxt can also attempt to determine the data type on its own, by giving the argument dtype=None. This works for complex values:

In [9]: genfromtxt('z.txt', dtype=None) Out[9]: array([[ 1.+2.j, -3.+4.j, 5.-6.j], [-1.+0.j, 0.+2.j, 3.+0.j]])
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