Linking data points

I know this is very basic but couldn't figure out how to.

I use this code to read data from my device;

clear all;
close all;
y = zeros(5000);
s1 = serial('/dev/ttyACM0');                   
s1.BaudRate=115200;                               
fopen(s1);
clear data;
for i= 1:20                             
    data=fscanf(s1);
    y(i) = str2double(data);
    fit = polyfit(i, y(i), 1)
    plot(fit,y(i))
    title('Data Output');
    xlabel('Points');
    ylabel('Values');
    drawnow;
    hold on
    if y(i) > 10
        fprintf(s1, '1');
    end
    if y(i) < 10
        fprintf(s1, '0');
    end   
end
fclose(s1);

And it works as expected. But it only shows points, not a plot. Not sure what is going on.

Answer 1

[Fangjun Jiang]

The way you did, every time it just plots one point (fit,y(i)).

Pre-allocate two vectors before the for-loop

N=20;
y=zeros(N,1);
fit=zeros(N,1);

Inside the for-loop, change it to

fit(i)=polyfit(i, y(i), 1)

Move all the following out of the for-loop:

    title('Data Output');
    xlabel('Points');
    ylabel('Values');
    drawnow;
    hold on

After the for-loop, run

plot(fit,y)

Answer 2

[Yigit]

It gives an error ;

Code ;

 clear all;
  close all;

s1 = serial('/dev/ttyACM0');                 
s1.BaudRate=115200;                             

fopen(s1);
clear data;

N=20;
y=zeros(N,1);
fit=zeros(N,1);

for i= 1:20                                
    data=fscanf(s1);
    y(i) = str2double(data);
    fit(i) = polyfit(i, y(i), 1);    
    title('Data Output');
    xlabel('Points');
    ylabel('Values');
    drawnow;
    hold on

      if y(i) > 10
          fprintf(s1, '1');
      end
      if y(i) < 10
          fprintf(s1, '0');
      end   

end

plot(fit,y)
fclose(s1);

Error ;

Warning: Polynomial is not unique; degree >= number of data points. 
> In polyfit at 71
  In dataq at 23
???  In an assignment  A(I) = B, the number of elements in B and
 I must be the same.

Error in ==> dataq at 23
    fit(i) = polyfit(i, y(i), 1);

[Fangjun Jiang]

fit() is actually a function, can you try to change the variable name?

[Yigit]

same behavior unfortunately.

Answer 3

[Walter Roberson]

You would get that error if you encountered a line that had a non-number, including at end of file (which you are not testing for)

Is there a particular reason to use fscanf() and then str2double() what you get from that? If you were going to use str2double() I would expect fgets() or fgetl(); if you were going to use fscanf() I would expect a format specifier to be given to it that would do the conversion.

Note that str2double() only processes a single value per string, never a vector of values per string. Because of that, you are doing a polyfit() on at most 1 value. That is not going to be very productive.