sparse_mkl backend integration

Author: maniospas

.gitignore

@@ -3,6 +3,7 @@ data/
 test.py
 github_ssh
 github_ssh.pub
+mkl_rt.2.dll
 
 
 # =================== PYCHARM ===================

pygrank/core/backend/sparse_dot_mkl.py

@@ -5,7 +5,17 @@
 import os
 if "MKL_NUM_THREADS" not in os.environ:
     os.environ["MKL_NUM_THREADS"] = str(os.cpu_count())
-import sparse_dot_mkl
+
+
+__pygrank_sparse_dot_mkl_warning = False
+try:
+    import sparse_dot_mkl
+except Exception as e:
+    __pygrank_sparse_dot_mkl_warning = True
+    warnings.warn("sparse_dot_mkl could not be imported.\n"
+                  "Please check your environment setup."
+                  "Falling back to numpy implementation for this backend.")
+    warnings.warn(str(e))
 
 
 def backend_init():
@@ -61,8 +71,6 @@ def self_normalize(obj):
         obj = obj / np_sum
     return obj
 
-__pygrank_sparse_dot_mkl_warning = False
-
 
 def conv(signal, M):
     global __pygrank_sparse_dot_mkl_warning