This gist provides a basic implementation on how you can use Matomo (Piwik) in a Search Site Collection

Matomo(Piwik)WithSharePointSearchCenter.js

var SpPiwik;
(function (SpPiwik) {
    SpPiwik.init = function () {
        window._paq = window._paq || [];
        /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
        window._paq.push(['enableLinkTracking']);
        if (typeof window._spPageContextInfo !== 'undefined'
            && window._spPageContextInfo.webServerRelativeUrl === '/suche'
            && typeof window.Srch !== 'undefined') {
            window._paq.push(['trackSiteSearch',
                // Search keyword searched for
                Srch.ScriptApplicationManager.get_current().queryGroups['Default'].dataProvider.get_currentQueryState().k,
                // Search category selected in your search engine. If you do not need this, set to false
                Srch.ScriptApplicationManager.get_current().queryGroups['Default'].dataProvider.get_sourceName(),
                // Number of results on the Search results page. Zero indicates a 'No Result Search Keyword'. Set to false if you don't know
                false
            ]);
        }
        else {
            window._paq.push(['trackPageView']);
        }
        (function () {
            var u = "//piwikserver.domain.de/";
            window._paq.push(['setTrackerUrl', u + 'piwik.php']);
            window._paq.push(['setSiteId', '1']);
            var d = document, g = d.createElement('script'), s = d.getElementsByTagName('script')[0];
            g.type = 'text/javascript';
            g.async = true;
            g.defer = true;
            g.src = u + 'piwik.js';
            s.parentNode.insertBefore(g, s);
        })();
    };
})(SpPiwik || (SpPiwik = {}));
(function () {
    window.onhashchange = function () {
        SpPiwik.init();
    };
})();