function addmarker(lat, long, flag) {

            iconFeature = new ol.Feature({
                geometry: new ol.geom.Point(ol.proj.transform([+long, +lat], 'EPSG:4326', 'EPSG:3857')),
                name: 'NULL'
            });

            iconStyle = new ol.style.Style({

                fill: new ol.style.Fill({
                    color: '#008000'
                }),
                stroke: new ol.style.Stroke({
                    color: '#008000',
                    width: 3
                }),
                image: new ol.style.Circle({
                    radius: 6,
                    fill: new ol.style.Fill({
                        color: '#008000'
                    })
                })

            });

            iconFeature.setStyle(iconStyle);

            vectorSource[flag] = new ol.source.Vector({
                features: [iconFeature]
            });

            vectorLayer[flag] = new ol.layer.Vector({
                source: vectorSource[flag]
            });

            map.addLayer(vectorLayer[flag]);

        }

function changemarker(lat, long, flag) {

             vectorSource[flag].clear();

            map.removeLayer(vectorLayer[flag]);

            addmarker(lat, long, flag);

        }