I want to use atan2 in my equation. When I use atan2 , I get answer NaN. But when I use 'atan' , i didn't get NaN. Why?

clear all 
clc 
syms alpha1 alpha1_d alpha1_dd
a=3;
b=2;
th1=atan2(a*sin(alpha1),(b*cos(alpha1)));
l1=a*cos(alpha1)*sin(th1)-b*sin(alpha1)*cos(th1);
l1_d=diff(l1,alpha1)*alpha1_d; % fisrt derivative of l1
l1_dd=jacobian(l1_d,[alpha1,alpha1_d])*[alpha1_d;alpha1_dd];% Sencond derivative of l1
% subs alpha1=0.5236, alpha1_d=0.2, alpha1_dd=0.01
L_dd=subs(l1_dd,[alpha1,alpha1_d,alpha1_dd],[0.5236,0.2,0.01]);

% Ans L_dd=NaN

%%%% when I replace atan2  by atan
clear all 
clc 
syms alpha1 alpha1_d alpha1_dd
a=3;
b=2;
th1=atan(a*sin(alpha1)/(b*cos(alpha1)));
l1=a*cos(alpha1)*sin(th1)-b*sin(alpha1)*cos(th1);
l1_d=diff(l1,alpha1)*alpha1_d;% fisrt derivative of l1
l1_dd=jacobian(l1_d,[alpha1,alpha1_d])*[alpha1_d;alpha1_dd];% Sencond derivative of l1
% subs alpha1=0.5236, alpha1_d=0.2, alpha1_dd=0.01
L_dd=double(subs(l1_dd,[alpha1,alpha1_d,alpha1_dd],[0.5236,0.2,0.01]));

% Ans L_dd=-0.1789

Answer 1

[Swatantra Mahato]

Hi Vishal,

You can try with "atan2" after making the following modifications

syms alpha1 alpha1_d alpha1_dd real

and add the line

l1=rewrite(l1,'sqrt');

before the line

l1_d=diff(l1,alpha1)*alpha1_d;

I have brought the issue to the notice of our developers. They will investigate the matter futher

Hope this helps

[Vishal Naik]

Sir, after additing the line 'l1=rewrite(l1,'sqrt')' before the line 'l1_d=diff(l1,alpha1)*alpha1_d', it doesn't work. I am getting the same answer 'NaN'.

Thank you...

[Paul]

Seemed to work for me:

>> syms alpha1 alpha1_d alpha1_dd real
a=3;
b=2;
th1=atan2(a*sin(alpha1),(b*cos(alpha1)));
l1=a*cos(alpha1)*sin(th1)-b*sin(alpha1)*cos(th1);
l1 = rewrite(l1,'sqrt');
l1_d=diff(l1,alpha1)*alpha1_d; % fisrt derivative of l1
l1_dd=jacobian(l1_d,[alpha1,alpha1_d])*[alpha1_d;alpha1_dd];% Sencond derivative of l1
% subs alpha1=0.5236, alpha1_d=0.2, alpha1_dd=0.01
L_dd=subs(l1_dd,[alpha1,alpha1_d,alpha1_dd],[0.5236,0.2,0.01]);
vpa(L_dd)
 
ans =
 
-0.17888259249992260757966824848436
 

[Vishal Naik]

It works. Thank you....