class_docstr: Hawkes kernel with sum exponential decays
  
  .. math::
      \phi(t) = \sum_{u=1}^{U} \alpha_u \beta_u \exp (- \beta_u t) 
                                 1_{t > 0}
  
  where :math:`\alpha_u` are the intensity of the kernel
  and :math:`\beta_u` its decays.
  
  Parameters
  ----------
  intensities : `np.ndarray`, shape = (n_decays, )
      Intensity of the kernel, also noted :math:`\alpha`
  
  decays : `np.ndarray`, shape = (n_decays, )
      Decay of the kernel, also noted :math:`\beta`
  
  Attributes
  ----------
  n_decays : `int`
      Number of decays of the kernel, also noted :math:`U`
class_docstr_tok: ["Hawkes","kernel","with","sum","exponential","decays","..","math",":",":","\\phi","(","t",")","=","\\sum_","{","u=1","}","^","{","U","}","\\alpha_u","\\beta_u","\\exp","(","-","\\beta_u","t",")","1_","{","t",">","0","}","where",":","math",":","`","\\alpha_u","`","are","the","intensity","of","the","kernel","and",":","math",":","`","\\beta_u","`","its","decays",".","Parameters","--","--","--","--","--","intensities",":","`","np.ndarray","`",",","shape","=","(","n_decays",",",")","Intensity","of","the","kernel",",","also","noted",":","math",":","`","\\alpha","`","decays",":","`","np.ndarray","`",",","shape","=","(","n_decays",",",")","Decay","of","the","kernel",",","also","noted",":","math",":","`","\\beta","`","Attributes","--","--","--","--","--","n_decays",":","`","int","`","Number","of","decays","of","the","kernel",",","also","noted",":","math",":","`","U","`"]
code: def n_decays(self):
      return self._kernel.get_n_decays()
  
file_path: tick/tick/hawkes/simulation/hawkes_kernels/hawkes_kernel_sum_exp.py
imports: import numpy
  from tick.hawkes.simulation.build.hawkes_simulation import HawkesKernelSumExp
  from .None import HawkesKernelExp
  from .hawkes_kernel import HawkesKernel
label_desc: Use image node_id 4 for calling the HawkesKernelSumExp obj's underlying member method code with example usage: obj.n_decays() and returns: self