i correctly wrote code for timer for due ?

Hello !

im using Due in Matlab.

with value change of writePosition fuctions.

together i want make plot in same time. so i used timer.

i correctly wrote but not work...

please help.

    clc; clear all; close all;                     %Reset all

a=arduino('COM4','Due','Libraries','Servo');   %Set Arduinio board
ai_pin='A6';                                   %Set Analog pin for ADC
s = servo(a, 'D7');

tic;                                           %Set stopwatch timer
i=0;                                           %Set i for measure length
pause(5);                                      %Delay 2 sec

time = str2num(get(handles.edit3,'String'));
step_input = 0.25;
writePosition(s, step_input); %1ms
pause(2);             
step_input(i) = 0.79;
writePosition(s, step_input(i))

%step_input(i) = 0.79;
%writePosition(s, step_input(i)); %2ms

while (toc<999)
  i=i+1;
  t(i)=toc;
  step_response(i)=readVoltage(a,ai_pin);    %Already voltages calculated

    figure(1)
    plot(t,step_response,'r');
    pause(0.1);
end