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#51 2010-09-19 11:53:01

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

YES, i HAVE USED THE SAME EQAUTION, GIVEN IN FORUM #50

IS IT OK?

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#52 2010-09-19 12:16:11

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

Yes, I believe so!

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#53 2010-09-26 04:19:52

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

thanks bobbym... can u also tell me wht is the formula to sove ln(x+y)

i mean how cn v open above equation like ln(xy)=ln(x)+ln(y)

wht is ln(x+y)=?

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#54 2010-09-26 04:36:52

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

Let me help with some terminology that may help clear this up. When we say solve we mean an equation. An equation has an equals sign in it.

Ex. y = 2x + 5 is an equation.

Phrases like ln(x+y) are expressions because they have no equals sign.
Although you can do ln(x*y) = ln(x) + ln(y) for certain values of x and y.
ln(x+y) doesn't have anything similar to that. We say it is in lowest terms or it is already simplifed.

There is this identity for it:

Now if you have an equation such as ln(x + y ) = 5 that I can solve by taking the exponential of both sides.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#55 2010-09-26 13:39:32

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

actually i dont want to solve equation for a specific solution. my problem is different. ok let me try to explain it.

I have this equation.

F(x, y) =    y log2(1+ x*z/N*B* y) + a (y  1)          ...........(1)

if we do derivative of eq (1) w.r.t y and equate it to 0 then it yields as follows:

ln (x*z / y) - x*z / y = __?___   ..............(2)

i want to find right hand side of equation (2), i know it is some constant but it is exactly equal to what? i want to find that. please help me out.

thanks..

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#56 2010-09-26 19:32:17

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

Is this what 1) is?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#57 2010-09-27 12:44:32

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

yes, eq(1) is same like this.

x is also multiplied by z in the numerator, rest is fine

Last edited by Neetu (2010-09-27 12:51:03)

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#58 2010-09-27 13:43:22

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

If:

I get this for the partial derivative with respect to y.

Set that to 0:

Clear the denominator:

Rearrange:

Where ln is the natural log,

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#59 2010-09-28 01:30:09

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

thanks... i want this equation somewht like equation 2... can u  solve it further.

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#60 2010-09-28 08:30:16

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi;

It is in equation 2's form.

ln (x*z / y) - x*z / y =

A fraction and a log. They are just switched.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#61 2010-10-01 10:06:21

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

thanks bobbym...

actualy i want exact solution as equation 2

the solution that you have given is like as follows

ln((x*z+BNy)/BNy)-x*z/(BNy+xz)=-aln(2)

we can leave BN according to my project, So now above equation becomes

ln((x*z+y)/y)-x*z/(y+x*z)=-aln(2) ....(3)

Now from above equation (3), i want to derive equation (2), left hand side should be same as in equation(2).

equation(2) is ln (x*z / y) - x*z / y = __?___

please try to solve my problem. thanks!

Last edited by Neetu (2010-10-01 10:09:52)

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#62 2010-10-01 16:15:33

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

You have several problems here. 3) Is not correct, it is not what I solved for. There is no minus sign in front of the a.

I can rearrange the equation to the form you want but it will not have a constant on the right.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#63 2010-10-01 20:29:39

DaveRobinsonUK
Member
Registered: 2010-04-24
Posts: 123

Re: Naturual Logarithms

Wow.. 3 pages! What have I started!

Hows things guys? Hope all is well

Can feel it coming together.. Slowly but Surely

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#64 2010-10-01 20:33:39

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Dave;

Yes, this is all your fault. Everybody knows I can not answer any question in under 400 000 words or posts, whichever is longer.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#65 2010-10-02 11:58:09

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

hi bobbym... equation (3) is modified from ur equation. I have rearranged it.

you please try to rearrange it to the required form.... if we dnt get constant at right hand side... dunno wry.... u please bring it to the required form by any means.

Thanks

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#66 2010-10-02 11:59:58

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

In equation (3), Left hand side is also different, that is why i put minus sign at the right hand side

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#67 2010-10-02 12:18:24

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

Yes, I see that now, sorry, my mistake. I can manipulate it to the form you want but the RHS will no longer just be -a ln(2).
It will have some variables on that side also.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#68 2010-10-03 00:03:09

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

Hi bobbym...

i dnt wnt variables at RHS. anyways you solve it the best you can. please drive LHS same as required. we can c RHS later on

Thanks

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#69 2010-10-03 10:38:35

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi Neetu;

Do you have any idea as to what values x,y,z are. Are either x or y or z likely to be close to 0?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#70 2010-10-03 10:44:42

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

y can be 0 or 1. while others are variables. x and z are variable less than 0

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#71 2010-10-03 10:47:59

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Hi;

So you are saying y is a boolean. It can only take two values?
Because that would be illegal.
Or are you saying it is between 0 and 1?

For the x and z are they large like  - 34, -321 or small like  - .274 ?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#72 2010-10-03 10:56:26

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

y can only take two values either 0 or 1

Sory in previous post, i hv written wrong. Actualy, x and z are variabes ranging between 0 to 1.

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#73 2010-10-03 10:59:39

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Naturual Logarithms

Okay but you see the problem when y is 0

equation(2) is ln (x*z / y) - x*z / y = __?___

That form you require is illegal. See the y in the denominator. You can not divide by 0. y = 1 is fine.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#74 2010-10-03 11:03:12

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

I also want to know do derivation rules chnages with summation. i mean wd dis symbol ∑

becuase the original equation is

F(x, y) =    ∑1 ∑2 y log2(1+ x*z/N*B* y) + a *(∑1 y  1)

∑1 represents summation ranges from p=1 to P

∑2 represents summation ranges from q=1 to Q

x, y and z are functions of p and q

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#75 2010-10-03 11:06:10

Neetu
Member
Registered: 2010-08-24
Posts: 35

Re: Naturual Logarithms

yes,  we are not goin to put values in this equation. that y in the denominator is nt a problem for my project