Problems with Plotting Matlab Function

Question

I am Beginner in Matlab, i would like to plot system concentration vs time plot at a certain time interval following is the code that i have written

%Input function of 9 samples with activity and time calibrated with Well %counter value approx : 1.856 from all 9 input values of 3 patients

function c_o = Sample_function(td,t_max,A,B)

   t   =(0 : 100  :5000); % time of the sample post injection in mins
   c   =(0 : 2275.3 :113765);

   A_max= max(c);   %Max value of Concentration (Peak of the curve)

   if (t >=0 && t <= td)
      c_o(t)=0;
   else if(td <=t && t<=t_max)
      c_o(t)= A_max*(t-td);
   else if(t >= t_max)
      c_o(t)=(A(1)*exp(-B(1)*(t-t_max)))+(A(2)*exp(-B(2)*(t- t_max)))+...
             (A(3)*exp(-B(3)*(t-t_max)));
   end

   fprintf('plotting Data ...\n');
   hold on;
   figure;
   plot(c_o);
   xlabel('Activity of the sample Ba/ml ');
   ylabel('time of the sample in minutes');
   title (' Input function: Activity sample VS time ');
   pause;
   end

I am getting following error

Operands to the || and && operators must be convertible to logical scalar values.

Error in Sample_function (line 18)
if (t >=0 && t <= td)

Kindly .Let me know if my logic is incorrect

Answer 1

您的t不是与0比较的单个值，因此无法评估为true或false。

Answer 2

t is written as a array of numbers. So, it can't be compared with a scalar value ex. 0. Try it in a for loop

for i=1:length(t)
   if (t(i) >=0 && t(i) <= td)
      c_o(t(i))=0;
   else if(td <=t(i) && t(i)<=t_max)
      c_o(t(i)))= A_max*(t(i)-td);
   else if(t(i) >= t_max)
      c_o(t)=(A(1)*exp(-B(1)*(t(i)-t_max)))+(A(2)*exp(-B(2)*(t(i)- t_max)))...
      +  (A(3)*exp(-B(3)*(t(i)-t_max)));

   end
end 

Answer 3

You want to do this with logical indexing

c_o = zeros(size(t));

c_o(t>=0 & t<=td) = 0; % this line is actually redundant and unnecessary since we initialized the vector to zeros
c_o(t>td & t<=t_max) = A_max*(t(t>td & t<=t_max)-td);
c_o(t>t_max) = (A(1)*exp(-B(1)*(t(t>t_max)-t_max)))+(A(2)*exp(-B(2)*(t(t>t_max)- t_max)))...
      +  (A(3)*exp(-B(3)*(t(t>t_max)-t_max)));

You could also make this a little prettier (and easier to read) by assigning the logical indexes to variables:

reg1 = (t>=0 & t<=td);
reg2 = (t>td & t<=t_max);
reg3 = (t>t_max);

Then, for instance, the second assignment becomes the much more readable:

c_o(reg2) = A_max*(t(reg2)-td);