stereoBM and SGBM not working

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I am trying to test the OpenCV classes stereoBM and StereoSGBM classes. when compiling the code below using

g++ main.cpp -o app pkg-config --cflags --libs opencv I get this error, fatal error: opencv2/contrib/contrib.hpp: No such file or directory

I am using Ubuntu 18.04 on an ARM platform (ODROID-XU4), and I have installed OpenCV version 3.2 using Synaptic Package Manager. The libraries are installed as indicated in the picture. However, I cannot locate contrib.hpp

#include "opencv2/core/core.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include "opencv2/contrib/contrib.hpp"  
#include <stdio.h>
#include <string.h>
using namespace cv;
using namespace std;
int main(int argc, char* argv[])
{
Mat g1, g2;
Mat disp, disp8;
char* method = argv[3];
g1 = imread(argv[1]);
g2 = imread(argv[2]);
//cvtColor(img1, g1, CV_BGR2GRAY);
//cvtColor(img2, g2, CV_BGR2GRAY);

if (!(strcmp(method, "BM")))
{
    StereoBM sbm;
    sbm.state->SADWindowSize = 9;
    sbm.state->numberOfDisparities = 112;
    sbm.state->preFilterSize = 5;
    sbm.state->preFilterCap = 61;
    sbm.state->minDisparity = -39;
    sbm.state->textureThreshold = 507;
    sbm.state->uniquenessRatio = 0;
    sbm.state->speckleWindowSize = 0;
    sbm.state->speckleRange = 8;
    sbm.state->disp12MaxDiff = 1;
    sbm(g1, g2, disp);
}
else if (!(strcmp(method, "SGBM")))
{
    StereoSGBM sbm;
    sbm.SADWindowSize = 3;
    sbm.numberOfDisparities = 144;
    sbm.preFilterCap = 63;
    sbm.minDisparity = -39;
    sbm.uniquenessRatio = 10;
    sbm.speckleWindowSize = 100;
    sbm.speckleRange = 32;
    sbm.disp12MaxDiff = 1;
    sbm.fullDP = false;
    sbm.P1 = 216;
    sbm.P2 = 864;
    sbm(g1, g2, disp);
}


normalize(disp, disp8, 0, 255, CV_MINMAX, CV_8U);

imshow("left", g1;
imshow("right", g2);
imshow("disp", disp8);

waitKey(0);

return(0);
}