The error occurs because you tried to access the second element of sidelobes when sidelobes only has one element. There are a lot of different reasons why it might only have one element, including that that is all that was ever put into there. There are a couple of more common reasons the problem might show up:
- comparisons were done on floating point numbers expecting equality between a computed value and a constant, or expecting equality between two computed values. Due to round-off problems, if you compute two floating point numbers in even trivially different ways the two numbers might come out unequal; floating point numbers should be compared to within a tolerance.
- an "if" was done on a condition that was being thought of as a scalar (a single value) but a vector or array was involved. When "if" is applied to a vector or array, the condition is only considered to be true if all values in the vector or array are non-zero ("true"). When this is not realized then it is common to end up with the variable undefined or with a variable assigned a scalar when it should be a vector.
