code: def gamma_expr(peak_location, peak_fwhm):
      shape, scale, coef = gamma_params(peak_location, peak_fwhm)
      return (
          coef
          * sympy.Piecewise((T + 1e-14, T >= 0), (0, True))
          ** (shape - 1)
          * sympy.exp(-(T + 1.0e-14) / scale)
      )
  
file_path: nipy/nipy/modalities/fmri/hrf.py
imports: from functools import partial
  import numpy
  import scipy.stats
  import sympy
  from sympy.utilities.lambdify import implemented_function
  from .utils import T, lambdify_t
label_desc: Use image node_id 2 for calling a global function with example usage: gamma_expr(peak_location, peak_fwhm) and returns: unknown