Re: Bit of help with arrays: Uni Homework.

"Anthony Keane" wrote in message <nu3slj$kdp$1@newscl01ah.mathworks.com>...
> Hey guys, I have been scratching my head for ages over this, I obviously don't want you to do my homework for me as I need to learn. But I have spent 17 hours on it...
> Many many variations made.
> Here's the question, and I will give you the code I have so far, and the problem I am having:
>
> The Question:
> ---------------------------------------------------------------------------------------------------------------------
> Vector of Body mass index (BMI) [1 Mark]
> BMI is defined by the formula: BMI = w/ h2, where w is the subject’s weight (in kg) and h is height (in metre). According to the World Health Organization (WHO), a person can be in one of the following states:
> - underweight, if his/her BMI is smaller than 18.5 (kg/m2)
> - normal weight, if BMI is not less than 18.5 and no more than 25
> - overweight, if 25<= BMI < 30
> - obesity, if BMI is no less than 30.
>
> Write a script file and save it with name MyFirstName_bmi_vect.m (replace MyFirstName with your own first name), to calculate the BMI and determine the weight state of a set of persons.
> 1) Create two variables (Weight and Height) to store a set of 100 values for weight in kg and height in meter, respectively. Use randi function to generate the values, e.g. randi([30, 80], 1, 100) generates 1 by 100 random integers in [30, 80]; randi([100,200], 1,100)/ 100 can generate 100 random numbers in [1.0, 2.0].
> 2) Calculate BMI value for the persons according to the formula, and store the values to variable BMI.
> 3) Plot the BMI values.
> 4) Use for loop and conditional statements to determine the BMI state of these 100 persons with regard to their BMI and WHO definition, and store their BMI states into a new vector StateBMI of size 1x100. The values stored in the vector StateBMI are set to one of the four values: 1, 2, 3 and 4, which correspond to states of underweight, normal weight, overweight and obesity, respectively.
>
> Run the script, test it, demonstrate it when ready, and record your program results.
> --------------------------------------------------------------------------------------------------------------------
>
> My better code so far:
> --------------------------------------------------------------------------------------------------------------------
>
> disp('Welcome to the BMI Calucluator')
> W = randi([30,80],1,100);
> h = randi([100,200], 1,100)/ 100;
> BMI=W/h.^2;
>
> for i=1:100;
> if (BMI<18.5);
> disp(BMI);
> elseif (BMI>18.5)&&(BMI<25);
> disp(BMI);
> elseif (BMI>=25)&&(BMI<=30);
> disp(BMI);
> elseif (BMI>30);
> disp(BMI);
> end
>
> end
>
> StateBMI=zeros(1,4);
> A=('Underweight');
> B=('NormalWeight');
> C=('Overweight');
> D=('Obese');
> ----------------------------------------------------------------------------------------------------------------
>
> Now the problem I am having is that it only calculates the BMI once and displays the same value 100 times in my code.
> My question is, how do I make it run the equation new each time for the 100 iterations and then store it into a 1*100 vector with 4 values?
> I can figure out the rest as soon as I can get to that point.
> Thank you in advance for your help, I have until Wednesday night to finish it (and one more, but the next question involves a similar problem).

Hi. BMI doesn't have 100 values because it is not being calculated as a vector as you need to vectorize both the division and power i.e. BMI=W/h.^2; is missing a period.

Also you should declare StateBMI=zeros(1,100); before the for loop say at the top of the code otherwise Matlab will have to resize the array 100 times.

Also some of your if elseif conditions are redundant. Try this as a partial solution for you to complete
 for i=1:100;
     if (BMI(i)<18.5);
     elseif (BMI(i)<25);
        StateBMI(i)=2;
     elseif (BMI(i)>=25)&&(BMI(i)<=30);
     else StateBMI(i)=4;
     end
 end
    disp(StateBMI);