Return of Natural log

Hi, I need to have returned in arduino the natural log of a random generated x number. How should the line code for obtaining the ln number should look like. Other forums mention the inclusion of a math.h library,

etc, but so far I am not getting what I need. I really appreciate help in this matter. Alex.

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balearicdynamics over 10 years ago +2

In your code you user ln10() ... In the cited reference, the two logarithm calculation methods are double log (double __x) // natural logarithm of x double log10 (double __x) // logarithm of x to base…
balearicdynamics over 10 years ago in reply to gadget.iom +2

Paul, only use double instead of long. Better avoiding too many casting and implicit conversions I think. That's ok, if the author has clear his request.
gadget.iom over 10 years ago +2

This is the latest version of the code I have worked with: double y = 0; void setup(){ Serial.begin(9600); randomSeed(analogRead(0)); } void loop() { double randNumber = random(300); y = log(randNumber…

gadget.iom over 10 years ago

Take a look at reply 4 here: Log functions not included in list of math functio
This may solve your issues.
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aureta over 10 years ago in reply to gadget.iom

Hi, I am including a snapshot of the code and serial monitor output. Still log of the x random number isn´t coming out with this code. I´ll appreciate help.
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clem57 over 10 years ago in reply to aureta

Looking at header it returns double not float. Arduino - H
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balearicdynamics over 10 years ago

In your code you user ln10() ...

In the cited reference, the two logarithm calculation methods are

double log (double __x) // natural logarithm of x
double log10 (double __x) // logarithm of x to base 10.

So the natural funciton is log, not log10() or I am wrong ?
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clem57 over 10 years ago in reply to balearicdynamics

Correct Enrico. Also you need to send a double and not an int value.
Clem
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aureta over 10 years ago in reply to clem57

sorry, but could you please tell how should the code look like. I am new in Arduino...
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balearicdynamics over 10 years ago in reply to aureta

Alejandro, please post your code and not a screenshot, so someone of us can replay with some correction...
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aureta over 10 years ago in reply to balearicdynamics

Thank you, here´s the code...

float y= 0;

void setup(){
Serial.begin(9600);

float lognx= 0;

randomSeed(analogRead(0));
}

void loop() {
// print a random number from 0 to 299
randNumber = random(300);
y= log10(randNumber);

// print a random number from 10 to 19
randNumber = random(10, 20);
Serial.print(randNumber); Serial.print("\t");
Serial.println(y);
delay(1000);
}
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balearicdynamics over 10 years ago in reply to aureta

Hello Alejandro,

First of all, please read how to use the editor, so we don't loose so much time finding comments in two posts and formatting your code.
I put your code below with my comments, so if you like you can try it

#include <math.h>

// Pay atention that you should have the math library in your Arduino IDE library path

double y=0; //float y= 0;

// Setup
void setup(){
Serial.begin(9600);
double lognx = 0; // float lognx= 0;
randomSeed(analogRead(0));

}

//////////////////////////
// Loop
//////////////////////////
void loop() {
// as we need a double to calc the ln while the random() generates a long interer it is better to cast it
y = log((double)random(300)); // y= log10(randNumber);

// print a random number from 10 to 19
long randNumber = random(10, 20);

Serial.print(randNumber); Serial.print("\t");
Serial.println(y);

delay(1000);
}

Please try this code.

A note on your logic that sound strange to me: why do you calculate the log on the random number 0-300 while then print another number between 10 and 19 ? Just to be sure that this is what you want.
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aureta over 10 years ago in reply to balearicdynamics

what I want is arduino to pick up a random number and for it, return their natural log. ...
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