Trouble with for-loop and fft

So the error I get in my code i am not understanding see attached code and error

Answer 1

[Dave B]

On line 33 of 'U296' you have the line

xdft=fft(signal.x_0_003{k},n)/L;

inside the fft you see:

signal.x_0_003{k}

but signal.x_0_003 is not a cell (or other type that supports {}).

What is class(signal.x_0_003)? Did you mean to use () instead of {}?

[shawn finley]

I am not sure what i need i am trying to interpert the fft over a time window.

[Dave B]

signal is a table

signal.x_0_003 is a variable in that table, my guess is that it contains a vector of values. You cannot use {} to index into this. I don't see how k would provide a time window here, but it's a little hard to say without knowing more about the structure of your table.

Here are some examples with table indexing that might help:

x=(10:10:100)';
t=table(x)

t = 10×1 table
     x 
    ___

     10
     20
     30
     40
     50
     60
     70
     80
     90
    100

k=3;
t.x(3)

ans = 30

t.x(k:k+5)

ans = 6×1

30 40 50 60 70 80

x2 = {1:5;5:10:30;1:3:12};
t=table(x2)

t = 3×1 table
         x2      
    _____________

    {[1 2 3 4 5]}
    {[  5 15 25]}
    {[ 1 4 7 10]}

t.x2{2}

ans = 1×3

5 15 25

[shawn finley]

thanks for the clairifacation on the indexing

Answer 2

[dpb]

What's the purpose of the loop over k?

You have the time history apparently as variable x_0_003 in the table which one presumes will be the third column.

If you want the FFT() of it, just write

xdft=fft(signal.x_0_003,n)/L;

There doesn't seem any point in the for...end loop at all.

NOTA BENE:

There's also no need to create copies of the table data into local variables time and volts; use the table variables directly. You could fix up the names in the table to be more meaningful either on input or later --

signal.Properties.VariableNames(2:3)={'Time','Volts'};

and then use

plot(signal.Time,signal.Volts)

[shawn finley]

The purpose of the for-loop is to analise the frequency that the fft generates over time.

I will look at using teh signal.Properties.VariablesNames code, but if it uses the signal tool box I don't have that.

[shawn finley]

Just to be clear I do not have the Signal Processing Toolbox, sorry and Thanks.