str2num results

Here is a test, please try it. I can't explain the reason. Thanks.

>> a='sss'
a =
    'sss'
>> b=str2num(a)
b =
     []
>> isnumeric(b)
ans =
  logical
   1
>> a='ss'
a =
    'ss'
>> b=str2num(a)
b =
  Empty state-space model.
>> isnumeric(b)
ans =
  logical
   0
>> a='ssa'
a =
    'ssa'
>> b=str2num(a)
b =
     []
>> isnumeric(b)
ans =
  logical
   1
>> 

[Geoff Hayes]

John - I saw this link Create state-space model, convert to state-space model which may be relevant given the 'ss' string and the 'Empty state-space model' message. Perhaps, under the hood, MATLAB is taking the 'ss' string and somehow creating a state space model (since ss is the function used to create a state space model).

Answer 1

[Fangjun Jiang]

ss() happen to be a function. You could run b=ss alone;

Answer 2

[Steven Lord]

From the documentation page for str2num: "In addition, str2num uses the eval function, which can cause unintended side effects when the input includes a function name. To avoid these issues, use str2double."

Neither sss nor ssa are functions in any MathWorks product.

ss is a function in Control System Toolbox.

Answer 3

[John]

Sometimes str2double gives error. Anyways, either way, How can we test if the input string is numeric? Like this:

>> a='notnumeric'

a =

'notnumeric'

>> b=str2double(a)

b =

NaN

>> isnumeric(b)

ans =

logical

1

The test says it's a numeric.