*Tutorial 3

*Learning Mata by example


*getting a subset of a matrix

*--------------Start Example  1 ----------------*

mata

a=(1,2,3\4,5,6\7,8,9)
a

b=a[2::rows(a), 2..cols(a)]   //note. :: for rows and .. cols
b

end

*--------------End Example------------------*
help m5_intro   // for help on rows() and cols()



*getting a subset of a matrix

*--------------Start Example  2 ----------------*

mata

a=(1,2,3\4,5,6\7,8,9)
a

b=a[(1::rows(a)-1), 2..cols(a)]   //note. :: for rows and .. cols
b

end

*--------------End Example------------------*
help m5_intro   // for help on rows() and cols()


*getting a subset of the matrix

*--------------Start Example  3 ----------------*

mata

a=(1,2,3\4,5,6\7,8,9)
a

b=a[(1+1)/2::rows(a), 2..cols(a)]
b
end

*--------------End Example------------------*


*getting a subset of the matrix

*--------------Start Example  4 ----------------*

mata

a=(1,2,3\4,5,6\7,8,9)
a

b=a[(1\3\2), (1,3)]
b 
end

*--------------End Example------------------*


  
*getting a subset of the matrix
 
*--------------Start Example  5 ----------------*

mata

a=(1,2,3,4,5,6,7\8,9,10,11,12,13,14\15,16,17,18,19,20,21\22,23,24,25,26,27,28\29,30,31,32,33,34,35\36,37,38,39,40,41,42\43,44,45,46,47,48,49)
a

b=a[|2,3 \ 4,7|]
b 
end

*--------------End Example------------------*
help m2_subscripts


**op_conditional -- Conditional operator

*--------------Start Example  6 ----------------*

mata

a=1
a

k=2
k


n=2
n


b=(a==1 ? n-1 : n-k)   //statement true then b=n-1
b 


b=(a==2 ? n-1 : n-k)    //statement false then b=n-k
b 

end

*--------------End Example------------------*
help m2_op_conditional


*Colon operators
*appling somehting to every element 
*--------------Start Example  7 ----------------*

mata

a=(1\2\3\4\5\6\7)
a

b=a :== 4 
b 


c=a :* b
c


d=b :* 10
d

end

*--------------End Example------------------*
help m2_op_colon




*exercise: if aa equals 4 then replace with 100

*--------------Start Example  8 ----------------*

mata

aa=(1\2\3\4\5\6\7)
aa

for (i=1; i<=rows(a);i++) {
if (aa[i]==4) {
aa[i]=100
}
}
aa

end

*--------------End Example------------------*



*exercise: if aa equals 4 then replace with 100

*--------------Start Example  9 ----------------*

mata

aa=(1\2\3\4\5\6\7)
aa

b= aa :==4
b

c=b :* 100
c

d= c :==0
d

e=d :+c
e

f=a :*e
f

end

*--------------End Example------------------*



**End of tutorial 3