MatLab help needed.

The problem is to find the intersection of two straight lines.

Namely, im working out the critical currenty density of corrosion in metal. But in any case, its a matter of solving for 1 unknown and I need your help.

Equations:
Vf1=Vf+Bflog(ic/if)
Vh1=Vh+Bhlog(ic/ih)

where,
Vf=-0.44
Bf=0.10
if=10exp-8
Vh=0
Bh=-0.08
ih=10exp-10

and we need to find ic,

can anyone help?

anyone?

Try the Maths forum

http://www.thestudentroom.co.uk/forumdisplay.php?f=38

Reply 3

didgeridoo12uk

have you actually written anything in matlab so far?

Reply 4

Nick Longjohnson

Give me a minute to do this.

And 10 mins to load matlab on my laptop

Reply 5

Peace0fM1nd

Original post by Nick Longjohnson

Give me a minute to do this.

And 10 mins to load matlab on my laptop

Reply 6

Nick Longjohnson

Original post by Peace0fM1nd

What range of ic are we looking at?

Reply 7

Peace0fM1nd

Original post by didgeridoo12uk

have you actually written anything in matlab so far?

YEs, but need more practice. i realised how i could use matlab to help me solve some corrosion problems, so im like using it on my own initiative - but i quickly found out how much practice i still need!! plus its amazing how many uses matlab actualy has!

Reply 8

Peace0fM1nd

Original post by Nick Longjohnson

What range of ic are we looking at?

10exp-4<ic>10exp4 (on logarithmic scale)

Reply 9

Nick Longjohnson

Original post by Peace0fM1nd

10exp-4<ic>10exp4 (on logarithmic scale)

My drunk/tired ass is having difficulty doing them now.

Im thinking of just making a function of Vf1-Vh1, and then using the fzero function to find where the difference is zero

Edit: I just plotted it to check, and it doesnt seem to cross within that range, unless im doing something wrong :s

(edited 13 years ago)

Reply 10

Peace0fM1nd

Original post by Nick Longjohnson

My drunk/tired ass is having difficulty doing them now.

Im thinking of just making a function of Vf1-Vh1, and then using the fzero function to find where the difference is zero

If it helps, i know that critical current density log(ic)= -2.446, i need to visualise the solution and. y axis will show V, x axis whill show ic. thanks for your help dude

Reply 11

Nick Longjohnson

Original post by Peace0fM1nd

If it helps, i know that critical current density log(ic)= -2.446, i need to visualise the solution and. y axis will show V, x axis whill show ic

I just did this to plot it, and it doesnt seem to cross (called if idotf so it doesnt interpret it as an 'if' statement :P):

Spoiler

Fzero is saying it goes into complex numbers:

root = fzero(@(ic)((-0.44+0.1*log(ic/(10^(-8))))-(0.08*log(ic/(10^(-10))))),0.01)

be advised: I havnt done matlab in a while and am very tired

(edited 13 years ago)

Reply 12

Peace0fM1nd

Original post by Nick Longjohnson

I just did this to plot it, and it doesnt seem to cross (called if idotf so it doesnt interpret it as an 'if' statement :P):

Spoiler

Fzero is saying it goes into complex numbers:

root = fzero(@(ic)((-0.44+0.1*log(ic/(10^(-8))))-(0.08*log(ic/(10^(-10))))),0.01)

be advised: I havnt done matlab in a while and am very tired