Symbols vs Floating points

This question has to do with the question in this link which Jan has kindly shed some light on.

http://www.mathworks.co.uk/matlabcentral/answers/33744-error-using-odearguments

As mentioned in my comment, I am wondering why my x0 is of class 'sym'. I tried playing around with it and discovered that the problem lies with c0=f(a0,b0).

But I don't know what I can do with it to make it a 'double'. The thing is c0 is a number, no?

[Richard]

When I run the code without c0, I get, for example

{x0 =

10 10}

class(x0)=double

whereas with c0, I get

{x0=

[10, 10, 20]}

,say, and

class(x0)=sym

So Matlab does get numbers, I don't know why the square brackets though and why the class.

[Jan]

Please post the definition of "f", "a0" and "bo". Otherwise we cannot guess what's going on.

[Jan]

The square brackets mean, that the value is a vector. I'm not sure, why the curly braces appear.

[Richard]

Thanks, Jan.

f = @(a,b) diff(100*a^5+b, sym('a'));

a0=10;

b0=10;

c0=f(a0,b0);

x0 = [a0,b0,c0];

The curly brackets aren't actually there (though the square ones are) -- I thought that using the curly ones in this forum gives the code font -- sorry it is really me being stupid!

[Jan]

The formatting in this forum is not intuitive.

Answer 1

[Jan]

Your f contains the term "sym('a')". Therefore the results get the type sym also. Perhaps you want to use the command double to make the symbolic expression numerically.

[Richard]

Hi, Jan, Thanks a lot! It is fixed now! :)