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From: michael caro on 4 May 2010 18:02
Can someone help me with this problem. I'll post the instructions, and
the code I've created.

Given the following equation: y=1/ sqrt [1+(αt)^2]

where 0 ≤ α ≤ 2 and 0 ≤ t ≤ 5. We would like to see how the plot of y
vs. t changes as the value of the parameter α changes. This is to be
done in the following manner:

Create an array of values for t using the range specified in
increments of 0.05 and an array for α (alpha) over the range specified
in increments of 0.5.

t=0:0.05:5;
a=0:0.5:2;

Find the number of values in the array, alpha, using the numel command
(see MATLAB help if you don’t remember it). Create an array Y to store
values to be plotted. The variable Y should have as many rows as there
are values of alpha and as many columns as there are values of t.

nt=numel(t);
na=numel(a);
Y=cell(na,nt);

Create a for loop that uses an indexing value from 1 to the number
values of alpha, found in (2) by the numel command. For each value of
‘α’, calculate the y values that correspond to the t values given the
equation from above with a vectorized equation. Save your results for
each value of alpha in each corresponding row of Y.

for i = 1:na
Y(a,:)=1./sqrt(1+(t.*a(i)).^2)
end

So i get the error, " Conversion to cell from double is not possible "

I really appreciate the help.
From: Nathan on 4 May 2010 18:09
On May 4, 3:02 pm, michael caro <mcaro1...(a)gmail.com> wrote:
> Can someone help me with this problem. I'll post the instructions, and
> the code I've created.
>
> Given the following equation: y=1/ sqrt [1+(αt)^2]
>
> where 0 ≤ α ≤ 2 and 0 ≤ t ≤ 5. We would like to see how the plot of y
> vs. t changes as the value of the parameter α changes. This is to be
> done in the following manner:
>
> Create an array of values for t using the range specified in
> increments of 0.05 and an array for α (alpha) over the range specified
> in increments of 0.5.
>
> t=0:0.05:5;
> a=0:0.5:2;
>
> Find the number of values in the array, alpha, using the numel command
> (see MATLAB help if you don’t remember it). Create an array Y to store
> values to be plotted. The variable Y should have as many rows as there
> are values of alpha and as many columns as there are values of t.
>
> nt=numel(t);
> na=numel(a);
> Y=cell(na,nt);
>
> Create a for loop that uses an indexing value from 1 to the number
> values of alpha, found in (2) by the numel command. For each value of
> ‘α’, calculate the y values that correspond to the t values given the
> equation from above with a vectorized equation. Save your results for
> each value of alpha in each corresponding row of Y.
>
> for i = 1:na
>     Y(a,:)=1./sqrt(1+(t.*a(i)).^2)
> end
>
> So i get the error, " Conversion to cell from double is not possible "
>
> I really appreciate the help.

Why is Y being indexed by a?
Do you mean Y(i,:)?

If so:

for i = 1:na
Y(i,:)={1./sqrt(1+(t.*a(i)).^2)} %note the braces
end

Is that what you were looking for?

-Nathan
From: Eric on 4 May 2010 18:17
You could just be lazy and let MATLAB handle your array sizing:

t=0:0.05:5;
a=0:0.5:2;
Y = [];
for i = 1:length(a)
Y=[Y;1./sqrt(1+(t.*a(i)).^2)];
end
From: michael caro on 4 May 2010 18:40
On May 4, 6:09 pm, Nathan <ngrec...(a)gmail.com> wrote:
> On May 4, 3:02 pm, michael caro <mcaro1...(a)gmail.com> wrote:
>
>
>
> > Can someone help me with this problem. I'll post the instructions, and
> > the code I've created.
>
> > Given the following equation: y=1/ sqrt [1+(αt)^2]
>
> > where 0 ≤ α ≤ 2 and 0 ≤ t ≤ 5. We would like to see how the plot of y
> > vs. t changes as the value of the parameter α changes. This is to be
> > done in the following manner:
>
> > Create an array of values for t using the range specified in
> > increments of 0.05 and an array for α (alpha) over the range specified
> > in increments of 0.5.
>
> > t=0:0.05:5;
> > a=0:0.5:2;
>
> > Find the number of values in the array, alpha, using the numel command
> > (see MATLAB help if you don’t remember it). Create an array Y to store
> > values to be plotted. The variable Y should have as many rows as there
> > are values of alpha and as many columns as there are values of t.
>
> > nt=numel(t);
> > na=numel(a);
> > Y=cell(na,nt);
>
> > Create a for loop that uses an indexing value from 1 to the number
> > values of alpha, found in (2) by the numel command. For each value of
> > ‘α’, calculate the y values that correspond to the t values given the
> > equation from above with a vectorized equation. Save your results for
> > each value of alpha in each corresponding row of Y.
>
> > for i = 1:na
> >     Y(a,:)=1./sqrt(1+(t.*a(i)).^2)
> > end
>
> > So i get the error, " Conversion to cell from double is not possible "
>
> > I really appreciate the help.
>
> Why is Y being indexed by a?
> Do you mean Y(i,:)?
>
> If so:
>
> for i = 1:na
>     Y(i,:)={1./sqrt(1+(t.*a(i)).^2)} %note the braces
> end
>
> Is that what you were looking for?
>
> -Nathan

Thank you for picking up on the mistake but thats not exactly what I'm
looking for.

How can I change the loop so matlab doesnt try to convert it into a
double?
i'd like to create an array with 5 rows and 101 columns. the 5 rows
correspond to each different 'a' variable being evaluated with all of
the 't' variables, so i can then create a plot saying plot(t,Y)

thanks once again
From: Walter Roberson on 4 May 2010 19:03
michael caro wrote:
> On May 4, 6:09 pm, Nathan <ngrec...(a)gmail.com> wrote:

>> If so:
>>
>> for i = 1:na
>> Y(i,:)={1./sqrt(1+(t.*a(i)).^2)} %note the braces
>> end


> Thank you for picking up on the mistake but thats not exactly what I'm
> looking for.

> How can I change the loop so matlab doesnt try to convert it into a
> double?

Nathan already answered that. Go back and reexamine the line, and "note the
braces". His solution already prevents matlab from trying to convert into a
double.

> i'd like to create an array with 5 rows and 101 columns. the 5 rows
> correspond to each different 'a' variable being evaluated with all of
> the 't' variables, so i can then create a plot saying plot(t,Y)

If you want to be able to do it with a single plot() call like you show, then
you *do* want the values converted to double -- plot can handle a numeric Y
array with multiple rows, but it cannot handle cell arrays to represent the rows.
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