Merge pull request #2805 from SinaHonari/issue2085

theano/scan_module/scan_op.py

@@ -288,14 +288,28 @@ class Scan(PureOp):
                  " does not match the number of inputs given to scan.")
         new_inputs = [inputs[0]]
         # assert dtype is consistent
-        err_msg1 = ('When compiling the inner function of scan the '
-                    'following error has been encountered: The '
+        err_msg1 = ('When compiling the inner function of scan (the '
+                    'function called by scan in each of its iterations) '
+                    'the following error has been encountered: The '
                     '%s %s (argument number %d) has dtype '
-                    '%s and %d dimension(s). The corresponding slice %s '
-                    'however has dtype %s and %d dimension(s) (it should '
-                    'have the same dtype and one fewer dimensions). This '
-                    'should never happen, please '
-                    'report to theano-dev mailing list'
+                    '%s and %d dimension(s). The corresponding variable '
+                    'in the inner function of scan %s '
+                    'however has dtype %s and %d dimension(s). This '
+                    'variable in the inner function of scan should '
+                    'have the same dtype and one fewer dimension '
+                    'compared to its corresponding variable in the initial '
+                    'state (outputs_info in scan nomenclature). For example, '
+                    'if the inner function of scan returns a vector '
+                    'of size d and scan uses the values of '
+                    'the previous time-step, then the initial state in scan '
+                    'should be a matrix of shape (1, d). '
+                    'The first dimension of this '
+                    'matrix corresponds to the number of previous time-steps '
+                    'that scan uses in each of its iterations. '
+                    'In order to solve this issue if the two variable currently '
+                    'have the same dimensionality, you can increase the '
+                    'dimensionality of the varialbe in the initial state of scan '
+                    'by using dimshuffle or shape_padleft. '
                    )
         err_msg2 = ('When compiling the inner function of scan the '
                     'following error has been encountered: The '
@@ -304,13 +318,26 @@ class Scan(PureOp):
                     'has dtype %s, while the result of the inner function '
                     '(`fn`) has dtype %s. This can happen if the inner '
                     'function of scan results in an upcast or downcast.')
-        err_msg3 = ('When compiling the inner function of scan the '
-                    'following error has been encountered: The '
+        err_msg3 = ('When compiling the inner function of scan (the '
+                    'function called by scan in each of its iterations) '
+                    'the following error has been encountered: The '
                     'initial state (`outputs_info` in scan nomenclature) '
                     'of variable %s (argument number %d) has %d dimension(s), '
-                    'while the result of the inner function (`fn`) has %d '
-                    'dimension(s) (should be one less than the initial '
-                    'state).')
+                    'while the corresponding variable in the result of the inner '
+                    'function of scan (`fn`) has %d dimension(s) (it should '
+                    'be one less than the initial state). For example, '
+                    'if the inner function of scan returns a vector '
+                    'of size d and scan uses the values of '
+                    'the previous time-step, then the initial state in scan '
+                    'should be a matrix of shape (1, d). '
+                    'The first dimension of this '
+                    'matrix corresponds to the number of previous time-steps '
+                    'that scan uses in each of its iterations. '
+                    'In order to solve this issue if the two varialbe currently '
+                    'have the same dimensionality, you can increase the '
+                    'dimensionality of the variable in the initial state of scan '
+                    'by using dimshuffle or shape_padleft. '
+                   )
 
         def format(var, as_var):
             """ This functions ensures that ``out`` has the same dtype as