fsolve usage

I would like to find help fixing my m-file and command windows. M-File that will determine the V0(initial velocity) and t(detonation time) necessary to hit a target.

input data: theta
            weight       %Weight of projectile  
            c            %Aerodynamic drag coefficient
return data: V0, t

function [V0,t]=offensive(theta,weight,c)
g=32.2;
weight=10;
theta=pi/6;
t=sqrt((2/g)*(300+5000*tan(theta)));
V0=[5000/(t*cos(theta))];
[V0,t]

command window

[V0,t]=fsolve(offensive,pi/6,10,0.1)

ans =  410.3725   14.0689

??? Error using ==> fsolve
FUN must be a function name, valid string expression, 
or inline function object.

Thanks.

Answer 1

[Walter Roberson]

[V0,t]=fsolve(@offensive,pi/6,10,0.1)

With the code you had, you were invoking the routine named "offensive" with no arguments, and passing the (numeric) result of that routine in as the first argument to fsolve.

Note that you will need to rewrite your routine "offensive" to use the parameters passed in to it instead of overwriting them in the routine.

[Nathanael]

How do you use fsolve? do you have to put @ on front. or it just indicating it is the function's name?.

When I am using what you wrote it gave me an error.

??? [V0,t]=fsolve(@

|

Missing variable or function.

[Walter Roberson]

How old is your MATLAB version? Anonymous functions were not supported in MATLAB 5 or some of MATLAB 6. You might have to code as

[V0,t] = fsolve('offensive',pi/6,10,0.1)

Answer 2

[Naz]

command line:

[Vo,t]=offensive(pi/6,10,.1)

Your function code does not make sense. You pass theta, weight, c to it, but then you rewrite 'weight' and 'theta' again inside the function. Then, I dont see you using these parameters - nor 'c', not 'weight' to calculate the V0 and t.

You are getting the answer because you did not comment the last line in the function code. Also, I dont think you need that line at all.

[Naz]

Is it necessary to use fslove?

[Walter Roberson]

If you are going to ignore the drag coefficient (as you do in your code) then there is no need to use fsolve: the equation can be solved analytically, such as is described at http://en.wikipedia.org/wiki/SUVAT_equations#Examples

My understanding is that once you introduce drag, you are solving a differential equation. You would not generally use fsolve() for differential equations, but perhaps this particular one can be done that way.

[Nathanael]

The problem states that I have use fsolve command.

[Walter Roberson]

If you show the calculation with drag included, I would have a better chance of analyzing the situation.