Sometimes it is necessary to estimate values that you can\'t measure easily from

Question

Sometimes it is necessary to estimate values that you can't measure easily from values that you can. For example, bone traits can usually only be measured accurately using non-invasive techniques like x-ray, CT scan, or MR1. This is expensive and time consuming, but if you can measure a large sample of people using these techniques, you can regress the data to develop an equation which relates (for example) a person's height to their tibia length. Two files have been uploaded: MaleTibiaData.txt and FemaleTibiaData.txt. They contain actual subject data from men and women. The first column is each person's height, h (in cm), the second column is their tibia length (in mm) measured from a CT scan. Write a function with header [tibl] = myTibia Length (height, sex) , where height is a user's height in cm and sex is either "m" or "f" The output argument will be a 2 TIMES 1 vector where tibL(l) = a1 + a2 h tibL( 2) =a1 + a2h + a3h2

Explanation / Answer

%Script file
MaleData=load('MaleTibiaData.txt');
FemaleData=load('FemaleTibiaData.txt');
% first column person height in cm
% second column is tibia length in mm
if MaleData<1 or FemaleData<1
disp('Tibia File open not successful');
exit(0);
end
MaleHeight=zeros(100,1);
MaleTibia=zeros(100,1);
sex='M';
countM=1;
while ~feof(MaleData)
MaleHeight(countM)=fscanf(MaleData,'%f',1);
[tiBL]=myTibiaLength(MaleHeight(countM),sex);
MaleTibia(countM)=tiBL(2);
countM=countM+1;
end
p = polyfit(MaleHeight,MaleTibia,2);
f1 = polyval(p,MaleHeight);
figure
plot(MaleHeight,MaleTibia);
hold on;
title('Male Height Vs Male Tibia');
plot(MaleHeight,f1);
xlabel('x-axis');
ylabel('y-axis');
hold off;
fclose(MaleData);

FemaleHeight=zeros(100,1);
FemaleTibia=zeros(100,1);
sex='F';
countF=1;
while ~feof(FemaleData)
height(countF)=fscanf(FemaleData,'%f',1);
[tiBL]=myTibiaLength(height(countF),sex);
MaleTibia(countM)=tiBL(2);
countF=countF+1;
end
p = polyfit(FemaleHeight,FemaleTibia,2);
f1 = polyval(p,FemaleHeight);
figure
plot(FemaleHeight,FemaleTibia);
hold on;
title('Female Height Vs Female Tibia');
plot(FemaleHeight,f1);
xlabel('x-axis');
ylabel('y-axis');
hold off;
fclose(FemaleData);

%=============================================

% function myTibiaLength.m
[tibL]=myTibiaLength(height,sex)
%height - user height in cm
%sex - m or f
%output is 2x1 vector

tibL=zeros(2,1);
tibL(1)=a1+(a2*height);
tibL(2)=a1+(a2*height)+(a3*height^2);

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