How to fix this. Please help!

//Question: Before interpolation the A matrix data i was unable to execute it because it was throwing error like A(2.6) for diffrent n(always integer) integers. Then i tried interpolating my matrix A . Its not giving proper results. Also i want my final answer to be displayed after for loop

t = 1 : 9;
t1= 1 : 0.1: 9;
A = [916.3 , 923.6 , 933.1, 947.4, 966.2, 986.6, 1008.5, 1031.5, 1051.3];  

A1= interp1( t , A, t1 , 'nearest');
a=1;
b=9;
n=6;
h=(b-a)/n;
for i = 0:3

      ans =0.5*[A1*(a+(i*h)) + A1(a+(i+1)*h)]*h;

end

[Azzi Abdelmalek]

"Thank you" is not a correct tag, please read this link http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

Answer 1

[Azzi Abdelmalek]

This line A1= interp1( t , A, t1 , 'nearest') is not correct, t is not defined, use

A1= interp1( time , A, t1 , 'nearest')

Add

a = 1;
b = 9;
n = 4;
h = (b-a)/n;
A = [916.3, 923.6, 933.1, 947.4, 966.2, 986.6, 1008.5, 1031.5, 1051.3 ];
for i = 0:3
res = 0.5 * [ A(a+(i*h)) + A(a+(i+1)*h) ]*h;
disp(res)
end

[Azzi Abdelmalek]

A(2.6) is not correct, the index should be a positive integer or logical.

If you want the value of A1 for t1=2.6,

A1(t1==2.6)

[Rizwana]

Hi: That was my typing mistake. Iam still getting not so correct value. Before interp1 function program is shown below: here the for loop executed 3 times and it displayed results because i have hand calculations it was matching. But this code was not working with variable n integers. Now iam not getting proper answer when i use interpolation

a = 1;

 b = 9;
 n = 4;
 h = (b-a)/n;

A = [916.3, 923.6, 933.1, 947.4, 966.2, 986.6, 1008.5, 1031.5, 1051.3 ];

for i = 0:3

 ans = 0.5 * [ A(a+(i*h)) + A(a+(i+1)*h) ]*h

disp('ans')

end

Thank You

[Azzi Abdelmalek]

a = 1;
b = 9;
n = 4;
h = (b-a)/n;
A = [916.3, 923.6, 933.1, 947.4, 966.2, 986.6, 1008.5, 1031.5, 1051.3 ];
for i = 0:3
res = 0.5 * [ A(a+(i*h)) + A(a+(i+1)*h) ]*h;
disp(res)
end

[Rizwana]

this wont work when i change n value to 5 or 6 or some other value also o/p is something like this:

res=

1.8494 e+003

1.8494 e+003

res=

1.8993e+003

1.8993e+003

res=

1.9747e+003

1.9747e+003

res=

2.059e+003

2.059e+003

// instead of multiple results i would like to have one res showing:

res=(1.8494 e+003)+(1.8993e+003)+(1.9747e+003)+(2.059e+003)

Thank You

[Azzi Abdelmalek]

%If a+(i*h)) and a+(i+1)*h represent time  
a = 1;
b = 9;
n = 5;
h = (b-a)/n;
t = 1 : 9;
A = [916.3, 923.6, 933.1, 947.4, 966.2, 986.6, 1008.5, 1031.5, 1051.3 ];
for i = 0:3
  res=0.5*h*(interp1(t,A,a+i*h)+interp1(t,A,a+(i+1)*h));
disp(res)
end

[Rizwana]

Here the matrix A represents presure quantities at time 1 to 9... i.e; A(1)=916.3---> presurre recorded at time 1sec A(2)=923.6---> presure recorded at time 2 sec... when i change n value to 5; then A in my program becomes A(1.6) This is throwing error... Hence i splitted the time array from 1:0.1:9 then interpolated the presuure data i.e ; A matrix to these values... Tried coding using program... Not getting answer with interpolated values... I tried to run your program.. Its throwing error: subscript indices must be real positive or logical... Thank You

[Azzi Abdelmalek]

I don't think you tried the correct program, copy ant paste the code in my previous comment. It works without errors

[Rizwana]

Thank You so much.