# modalities.fmri.spm.trace

## Module: `modalities.fmri.spm.trace`

nipy.modalities.fmri.spm.trace.trRV(X=None, V=None)

  If V is None it defaults to identity.

  If X is None, it defaults to the 0-dimensional subspace, i.e. R is the identity.

      >>> import numpy as np
      >>> from numpy.random import standard_normal
      >>>
      >>> X = standard_normal((100, 4))
      >>> np.allclose(trRV(X), (96.0, 96.0))
      True
      >>> V = np.identity(100)
      >>> np.allclose(trRV(X), (96.0, 96.0))
      True
      >>>
      >>> X[:,3] = X[:,1] + X[:,2]
      >>> np.allclose(trRV(X), (97.0, 97.0))
      True
      >>>
      >>> u = orth(X)
      >>> V = np.dot(u, u.T)
      >>> print(np.allclose(trRV(X, V), 0))
      True