Recommended problems

Try to avoid loops!

1. problem: Plot the distribution of the bmi indecies (weigth in kg / heigth^2 in meters) according to the adatok.csv file. Find out, that

How many people have bmi under 18?

How many people have bmi over 25?

How many people have bmi between 18 and 25?

ad=dlmread('adatok.csv');

bmi=ad(:,2)./ad(:,1).^2*1e4;

lessthan18=sum(bmi<18)
morethan25=sum(bmi>25)
between1825=sum(bmi<=25 & bmi>=18)

lessthan18 =

   593


morethan25 =

       15057


between1825 =

        4350

2. problem: Answer the qustions above for people under 30 years.

young=ad(:,3)<30;
youngbmi=ad(young,2)./ad(young,1).^2*1e4;

lessthan18=sum(youngbmi<18)
morethan25=sum(youngbmi>25)
between1825=sum(youngbmi<=25 & youngbmi>=18)

lessthan18 =

    93


morethan25 =

        2541


between1825 =

   683

3. problem: Try plotting the A=[3 4 2 3; 1 3 5 1; -9 5 2 5] matrix. Explain, what you see on the plot.

Each column is plotted with one line.

4. problem: Plot the parametrized curve x(t)=t*cost(t), y(t)=t*sin(t) while t is between 0 and 10. Label the axis, give our plot a title and save it as a jpg file.

function spiral

t=linspace(0,10,100);
plot(t.*sin(t),t.*cos(t))
xlabel('x axis')
ylabel('y axis')
title('Spiral')
saveas(gca,'snail.jpg')

5. problem: Write a function called funSign, which takes thwo number as input: a and b. The function should plot the sine function on the [a,b] interval, and it's output should be 1 if the sign of the sine function is different in the point a and b, 0 is any of a or b is a root, -1 otherwise.

function out1=funSign(a,b)

t=linspace(a,b);
plot(t,sin(t))

if sin(a)*sin(b)<0
    out1=1;
elseif sin(a)*sin(b)==0
    out1=0;
else
    out1=-1;
end

6. problem: Plot a half sphere.

function halfSphere

x=linspace(-1,1); 
y=x; 
[xx,yy]=meshgrid(x,y);

z1=1-xx.^2-yy.^2;
z1(z1<0)=0;
z1=-sqrt(z1);


mesh(x,y,z1)