code: def _covar_func(x1, x2, **kwargs):
      x1_, x2_ = _lazify_and_expand_inputs(x1, x2)
      K = (-((x1_ - x2_) ** 2).sum(-1) / 2).exp()
      return K
  
imports: from linear_operator.operators import KernelLinearOperator
  from .keops_kernel import _lazify_and_expand_inputs, KeOpsKernel
label_desc: Use image node_id 1 for calling a global function with example usage: _covar_func(x1, x2) and returns: K