Add error for out of range strain mode order

Add error to handle case when absolute value of the mode's order
exceeds its degree.

lvcnrpy/format/errors.py

@@ -87,3 +87,12 @@ class Missing(Error):
     """No value is defined for the field"""
     name = "MISSING"
     msg = None
+
+
+class InvalidModeName(Error):
+    """Mode's absolute order value exceeds degree"""
+    name = "INVALID MODE"
+    msg = "(Order {0:} of mode is not allowed for degree {1:})"
+
+    def __init__(self, spec):
+        self.msg = self.msg.format(spec.m, spec.l)

lvcnrpy/format/specs.py

@@ -594,6 +594,13 @@ class Phaselm(ROMSplineSpec):
 
         return SubPhaselm
 
+    @classmethod
+    def valid(self, sim):
+        if abs(self.m) > self.l:
+            return err.InvalidModeName(self)
+        else:
+            return super(Phaselm, self).valid(sim)
+
     @classmethod
     def getlm(self, sim):
         """Get a list of phase modes available in an LVC NR simulation
@@ -677,6 +684,13 @@ class Amplm(ROMSplineSpec):
 
         return SubAmplm
 
+    @classmethod
+    def valid(self, sim):
+        if abs(self.m) > self.l:
+            return err.InvalidModeName(self)
+        else:
+            return super(Amplm, self).valid(sim)
+
     @classmethod
     def getlm(self, sim):
         """Get a list of amp modes available in an LVC NR simulation