# Tweaking an equation!

#### skiddy

##### New member
Ive seen this picture and equation, and im trying to recreate it using datum curves and equations...

The equation is

a=1

b=0.2

v=12.56

u=2

x=a*cos(v)*sin(u)

y=a*sin(v)*sin(u)

z=a*(cos(u)+log(tan(u/2)))+b*v

View attachment 42

I think it needs some tweaking, pro e accepts it as no errors in the equation but it needs resolving it cant be created as yet! Any ideas?

I wasnt sure if pro e accepted the term 'log' ?

Thanks

=)

#### nkpham

##### New member
this wouldn't work because it would only give you one point.... there is no variable being varied. all the variables are listed as constants. are you sure the equation is correct?

to get a list of functions you can use, type in functions used in relations in the pro e help search.

and sorry.... i do not have any of the equations i've used to give you.

#### kvision

##### Moderator
a=2

b=0.2

v=4*360

u=120

x=a*cos(v*t)*sin(u*t)

y=a*sin(v*t)*sin(u*t)

z=a*(cos(u*t)+log(tan(u*t/2)))+b*v*t

Make sure it is in DEGREES not radians and make sure you vary the correct parameters. The curve looked small so you can make a bigger to enlarge it. Good luck.

KVision

#### Rajesh

##### New member
kvision

The above said equation is giving an error in the last line, z.

Can you give us the corrected one.

#### Tunalover

##### New member
I recommend checking the math.

If z=a*(cos(u*t)+log(tan(u*t/2)))+b*v*t, then the argument ut/2 may only aproach 90 + 180m where m is zero, a positive integer, or a negative integer.

Secondly, if the log(tan(ut/2)) term is to be bounded, then

tan(ut/2) may never be negative or zero. Put another way, arctan(ut/2) must be greater than zero. If 't' is a parametric variable that goes from -1 to 1, be careful! Check your range of 't' to insure that the tan(ut/2) and the log(tan(ut/2)) terms don't blow up.

#### kvision

##### Moderator
The equations work as given for me. It just gave me a tight spiral. I didn't make an effort to check all of the math initially sincee I read that the equation was given somewhere else from a working model. t is a parameter that goes from 0 to 1.

I copied the equation from this forum and got the following curve.

View attachment 250