Matlab error Undefined function or method 'du' for input arguments of type

[bora b. (borabora2012)]

Hi,

I have written that equations but I got an error at the end...

A=0.05;
rho=1.225;
t=0.001;
v=5;
Cu(1)=1.3;
Cl(1)=0.34;
u(1)=0;
a(1)=0;
i=2:1000;
u(i)=u(1)+du(i);
da(i)=ds(i)*360/0.628;
ds(i)=du(i)*t;
a(i)=da(i)+a(i-1);
du(i)=F(i-1)*0.001/0.05;
F(i-1)=(F1(i-1)-F2(i-1))*cos(a(i-1));
F1(i-1)=0.5*1.225*Cu(i-1)*A(i-1)*(v-u(i-1))^2;
F2(i-1)=0.5*1.225*Cl(i-1)*A(i-1)*(v+u(i-1))^2;
A(i-1)=A*cos(a(i-1));
Cu=-0.0053*a(i-1)+1.3;
Cl(1)=0.0053*(180+a(i-1));

??? Undefined function or method 'du' for input arguments of type
'double'.

Error in ==> Scientific at 10
u(i)=u(1)+du(i);

thanks a lot...

[Jan S. (spongebob)]

Line 10 is "u(i)=u(1)+du(i);" as you say.
In the lines before you never define "du".
How should Matlab know what to do with that variable? You must define it 
before you work with it.

[bora b. (borabora2012)]

ok thanks... i thought that it is a much complex problem...

I have to correct all the sequence of the equations. I have to write 
also in the physical way for my anemometer simulation...

[Kevin K. (nemon)]

This Program shall work if you place line
du(i)=F(i-1)*0.001/0.05;
before line
u(i)=u(1)+du(i);

[bora b. (borabora2012)]

A(1)=0.05;
rho=1.225;
t=0.01;
v=5;
u(1)=0;
a(1)=0;
C(1)=1.3;
for i=2:1000
C(i-1)=0.82+0.48*cos(a(i-1));
A(i-1)=A(1)*cos(a(i-1));
F1(i-1)=0.5*1.225*C(i-1)*A(i-1)*(v-u(i-1))^2;
F2(i-1)=0.5*1.225*C(i-1)*A(i-1)*(v+u(i-1))^2;
F(i-1)=(F1(i-1)-F2(i-1))*cos(a(i-1));
du(i)=F(i-1)*0.001/0.05;
u(i)=u(1)+du(i);
ds(i)=du(i)*t;
da(i)=ds(i)*2*pi/0.628;
a(i)=da(i)+a(i-1);
end


i corrected the codes in that way...C(1)=1.3; does not make sense but I 
left it...

the first line and the last one

C(i-1)=0.82+0.48*cos(a(i-1));
..
a(i)=da(i)+a(i-1);            depend on eachther. that is why i wrote if 
end loop. I dont get any fault but my problem is that I got the constant 
values for all variables in my Workspace.

thanks a lot

[bora b. (borabora2012)]

for each variable I got this error

The variable 'F2' appears to change size on every loop iteration (within 
a script). Consider preallocating for speed

Explanation
The size of the indicated variable or array appears to be changing with 
each loop iteration. Commonly, this message appears because an array is 
growing by assignment or concatenation. Growing an array by assignment 
or concatenation can be expensive. For large arrays, MATLAB must 
allocate a new block of memory and copy the older array contents to the 
new array as it makes each assignment.
Programs that change the size of a variable in this way can spend most 
of their run time in this inefficient activity. There is also 
significant overhead in shrinking an array on each iteration or in 
changing the size of a variable on each iteration. In such cases, MATLAB 
must reallocate and copy the contents repeatedly.
For scripts, M-Lint cannot determine whether the array was preallocated 
before the script was called. Depending on your use of scripts, you 
might want to enable or disable this message independently of the 
related message (with message ID AGROW) that applies to functions and 
class methods.
 Suggested Action
Consider preallocating a variable or array before entering the loop by 
using zeros, ones, cell, or a similar function. Preallocating avoids the 
need for MATLAB to copy the data from one array to another inside the 
loop. For examples of code that do and do not preallocate an array, see 
“Preallocating Arrays”
When an array grows by assigning past the end of the array or using 
concatenation, preallocation alone does not improve the performance. The 
code must use explicit indices also.
Assigning to an array in a script that the caller of the script 
preallocated provides an opportunity to create bugs that are difficult 
to detect. If the script is called multiple times, these bugs are 
particularly difficult to detect. However, there are other uses of 
scripts where preallocating in this manner is necessary or even 
desirable. In this case, suppress the message for specific assignments 
or for the whole script, as described in “Suppressing M-Lint Indicators 
and Messages”. It might also be appropriate to suppress this message if 
any of the following is true:
The loop code is searching for rare or exceptional events (especially if 
you do not expect it to find any).
In this case, it can be reasonable to grow the array only as the loop 
code finds such events.
The array is small and will always be small.
In this case, the impact of recopying is also small.
The array was preallocated, but in a way that M-Lint does not recognize.
If you do not know the size of an array before the loop begins, 
preallocate it, and then shrink it, if necessary, after the loop 
completes.

[J.-u. G. (juwe)]

bora bora schrieb:
> for each variable I got this error
>
> The variable 'F2' appears to change size on every loop iteration (within
> a script). Consider preallocating for speed

This is not an error message, but a suggestion for speed increase.

> Consider preallocating a variable or array before entering the loop by
> using zeros, ones, cell, or a similar function.
> ...
> For examples of code that do and do not preallocate an array, see
> “Preallocating Arrays”

And, did you read this help item?

[bora b. (borabora2012)]

Yes I read.

I looked at this links

http://www.mathworks.de/support/solutions/en/data/1-18150/

http://www.mathworks.de/de/help/matlab/matlab_prog/techniques-for-improving-performance.html

I tried to apply it also for my file like that:

C=zeros(1000);
A=zeros(1000);
F1=zeros(1000);
F2=zeros(1000);
F=zeros(1000);
du=zeros(1000);
u=zeros(1000);
ds=zeros(1000);
da=zeros(1000);
a=zeros(1000);

However, I see now only matrixes and the first column is for C for 
example only 1.3 and the other all columns are zero. It didnt solve my 
problem I see again constant values but I have know matrix with zeros... 
I couldnt solve yet.

[J.-u. G. (juwe)]

bora bora schrieb:
> C=zeros(1000);
> A=zeros(1000);
> F1=zeros(1000);
> F2=zeros(1000);
> F=zeros(1000);
> du=zeros(1000);
> u=zeros(1000);
> ds=zeros(1000);
> da=zeros(1000);
> a=zeros(1000);

> I see now only matrixes

Every Matlab command has its own help item. Its on you to use this help. 
From the help text of the "zeros" command:
http://www.mathworks.com/help/matlab/ref/zeros.html:

> B = zeros(n) returns an n-by-n matrix of zeros. An error
> message appears if n is not a scalar.
>
> B = zeros(m,n) or B = zeros([m n]) returns an m-by-n matrix
> of zeros.

What do you think will "C=zeros(1000)" do?

[bora b. (borabora2012)]

Ok. it changes my C value to a matrix as it should be... it is ok...
I have to check my algorith I think... because of the equations I cannot 
get variable values maybe.